Variable roles of interleukin-17F in different cancers

Interleukin (IL)-17 family is a group of six cytokines that plays a central role in inflammatory processes and participates in cancer progression. Interleukin-17A has been shown to have mainly a protumorigenic role, but the other members of the IL-17 family, including IL-17F, have received less attention. We applied systematic review guidelines to study the role of IL-17F, protein and mRNA expression, polymorphisms, and functions, in cancer. We carried out a systematic search in PubMed, Ovid Medline, Scopus, and Cochrane libraries, yielding 79 articles that met the inclusion criteria. The findings indicated that IL-17F has both anti- and protumorigenic roles, which depend on cancer type and the molecular form and location of IL-17F. As an example, the presence of IL-17F protein in tumor tissue and patient serum has a protective role in oral and pancreatic cancers, whereas it is protumorigenic in prostate and bladder cancers. These effects are proposed to be based on multiple mechanisms, such as inhibition of angiogenesis, vasculogenic mimicry and cancer cell proliferation, migration and invasion, and aggravating the inflammatory process. No solid evidence emerged for the correlation between IL-17F polymorphisms and cancer incidence or patients’ prognosis. IL-17F is a multifaceted cytokine. There is a clear demand for more well-designed studies of IL-17F to elucidate its molecular mechanisms in different types of cancer. The studies presented in this article examined a variety of different designs, study populations and primary/secondary outcomes, which unfortunately reduces the value of direct interstudy comparisons.


Introduction
Cancer caused almost 9.6 million deaths globally in 2018 [1]. The incidence of cancers can be decreased to some extent by avoiding known risk factors, such as tobacco smoking and alcohol consumption [2], but several unknown environmental, genetic, and epigenetic reasons likely exist for cancer progression. Thus, safer and more effective treatments are continuously being sought for different cancer types.
Cancer biomarkers are biological compounds detectable in tissues or body fluids. They are applied for the prognosis of various cancers and to predict the outcome and efficiency of treatments [3]. Cytokines, one group of biomarkers, are proteins that participate in cell signaling and mediate innate and adaptive immune system responses. Some cytokines, such as interleukin (IL)-2 and IL-15, seem to also be relevant in cancer immunotherapy [4].
Interleukin (IL)-17F is a member of the IL-17 cytokine family, which contains six members (IL-17A-F). IL-17F is produced by several cells, including activated CD4 + T cells, monocytes, basophils, and mast cells [5]. IL-17A and IL-17F share the greatest homology with each other, and they have two common receptors: IL-17RA and IL-17RC. IL-17A was the first IL-17 cytokine identified, and it plays important roles in host defense, inflammation, allograft rejection, and autoimmune diseases such as psoriasis [6][7][8]. IL-17A has mainly been reported as a protumorigenic factor, however some studies showed it as an antitumorigenic cytokine [6,9]. Other members, including IL-17F, have been far less extensively studied, also in cancer [10].
Here, we systematically collected literature concerning the expression, polymorphisms, and function of IL-17F in various cancers and reviewed the role of IL-17F as a pro-or antitumorigenic molecule. We also analysed data related to the proposed molecular mechanisms by which IL-17F affects cancer development and progression.

Methods
This review study was registered at the international prospective register of systematic reviews PROSPERO under registration number CRD42020186465.
We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and conducted a search using PubMed, Ovid Medline, Scopus, and Cochrane Library databases. We searched the terms interleukin-17F (interleukin 17f OR il 17f OR interleukin-17f OR il-17f) and cancer (cancer OR neoplasm* OR carcinoma* OR malignan* OR tumo?r* OR sarcoma* OR leukemia* OR lymphoma* OR adenocarcinoma*), with an asterisk (*) indicating truncation and a question mark (?) indicating wildcard characters, from titles, abstracts, and keywords. We conducted two searches, the first one was on the 15th of May 2020, and the second search covered the period from 16th of May 2020 until 9th of October 2021.
We identified a total of 1146 records through database searching and removed 310 duplicates, leaving 836 records for screening. Three researchers (R.A. and T.M. or A.A.) screened the records independently and were blinded to each other's decisions. Disagreements in included and excluded articles were resolved by reaching a consensus between the researchers. We excluded 736 records because they were reviews, case reports, letters, book chapters, conference abstracts, written in languages other than English, or irrelevant to our review. In addition, we found a few more duplicates during manual record screening. We assessed 100 full-text articles for eligibility, excluded a further 21, and thus, included 79 articles in this review (Fig. 1). We recorded all data extraction results using Excel.
We extracted all data concerning cancer type, study size, methodology, and main findings with p-values from the articles. We included study population in the extraction of IL-17F polymorphism studies.

Protein and mRNA expression of IL-17F in various cancers
We present the studies on IL-17F mRNA and protein expression levels in Table 1 based on cancer type listed alphabetically. Below, we describe the results in the order of the most studied cancers of each category.

IL-17F expression is linked to colorectal cancer
The expression of IL-17F has been investigated most in colorectal cancer (CRC) [14][15][16][17][18][19][20]43]. IL-17F expression in CRC tissue samples was studied in 4 articles [15,16,20,43]. In three articles, IL-17F expression in tumour sections was decreased [16,20,43]. Al-Samadi et al. [43] showed by immunohistochemistry that IL-17F level was decreased in CRC compared with healthy controls, and similarly, Liu et al. [16] found less IL-17F in CRC than in ulcerative colitis or polyp samples. In addition, IL-17F mRNA expression was reduced in colon cancer according to Tong et al. [20]. However, Chen et al. [15] reported recently that IL-17F was overexpressed in tumour mucosa compared with paired non-tumour mucosa. Serum levels of IL-17F in CRC patients were studied in 3 articles [17][18][19]. In one publication, elevated serum, together with conditioned media from cultured surgical resection, levels of IL-17F were associated with advanced colon cancers [18], whereas no association between serum levels and overall survival or progression-free survival among CRC patients was detected in another publication [17], and in a third publication, no detectable IL-17F levels in CRC patients' serum were found [19].
Heeran et al. [14] showed that IL-17A/F secretion from the cultured rectal cancer biopsy was significantly higher than the normal rectal tissue, however the study did not report the level of IL-17F alone.
IL-17F has mainly a protective role in oral squamous cell carcinoma, but not in skin basal cell carcinoma Four articles investigated the expression of IL-17F in oral cancers [22,23,44,45]. Three articles reported a protective role of IL-17F in oral cancer while the fourth one suggested a protumorgenic effect for IL-17F. Extracellular IL-17F at the tumour invasion front was associated with better disease-specific survival among oral tongue squamous cell carcinoma (OTSCC) patients [44]. In two studies, serum-derived IL-17F was decreased in OSCC patients compared with healthy controls [22,23]. On the other hand, the concentration of IL-17F in the saliva of oral and oropharyngeal cancer patients was significantly associated with disease progression [45]. To conclude, IL-17F protein in tissue and serum, but not in saliva, seems to possess an antitumorigenic role in oral cancers. By contrast, in skin basal cell carcinoma, serum levels of IL-17F were not associated with cancer risk [42].
Two studies addressed the role of IL-17F in chronic lymphocytic leukaemia (CLL) [24,25]. The first publication showed an increase in serum IL-17F in stage IV B-CLL patients compared with healthy controls and stage 0/I and III patients [25]. The same study found a lower IL-17F expression in PMNs and B-lymphocytes of patients compared to cells of healthy subjects [25]. The second study reported no significant association between TH17F + cells and CLL [24].

No consensus on IL-17F levels in lung cancer
Regarding lung malignancies, we found three studies in which IL-17F was measured [28][29][30]. Huang et al. [29] documented that IL-17F immunoreactivity was increased in both squamous cell carcinoma and adenocarcinoma tissues compared with healthy controls. In contrast, according to Li et al. [28], IL-17F was positively associated with tumour differentiation and negatively with lymph node metastasis and TNM staging. Similarly, Yang et al. [30] found that IL-17F, in the patients' serum, was decreased in more progressive disease.

Amount of IL-17F varies in breast, ovarian, and prostate cancers
Two studies have analysed IL-17F protein amount in breast cancer patients [12,13]. Oda et al. [13] noted that IL-17F + tumour infiltrate T-cells were associated with smaller tumour size. Avalos-Navarro et al. [12] did not find an association between serum IL-17F expression and breast cancer. In ovarian cancer, levels of IL-17F + Th17-cells were similar between cancer and control groups [37], and IL-17F in the ascites fluid was not associated with patients' overall survival [38]. As for prostate cancer, two studies reported that  Janiczek et al. 2020 [40] surgical resection Protein IHC 29 (prostate adenocarcinoma) + 47 (BPH) + 6 (control) IL-17F was elevated in BPH (p = 0.014) and prostate adenocarcinoma (p = 0.026) compared to healthy controls.
Expression of IL-17F in liver, pancreatic, and bladder cancers varies In liver cancer, one study reported no association between IL-17F protein levels and hepatocellular carcinoma [26], whereas another one suggested that IL-17F mRNA was more often present in cancerous than in adjacent non-cancerous tissue of hepatitis C virusassociated hepatocellular carcinoma [27]. IL-17F was decreased in patients with pancreatic adenocarcinoma compared with chronic pancreatitis patients [39]. In bladder cancer, IL-17F was overexpressed in the cancer group compared with the cystitis and hyperplastic bladder polyp groups [11].
To summarize, IL-17F expression (protein and mRNA) levels in tumour and serum samples seem to depend on cancer type (Fig. 2), and more studies are needed prior to concluding its predictive value in any of the malignancies.

Proposed function of IL-17F based on in vivo and in vitro studies
We analysed the mechanisms by which IL-17F affects cancer development and progression based on in vitro and in vivo animal studies and collected the findings in Table 4.

Mechanisms for antitumour effects of IL-17F
Several mechanisms have been suggested through which IL-17F exert its antitumorigenic effects, including inhibition of tumour angiogenesis, cell cycle regulation, cancer cell proliferation and migration, and cancer vasculogenic mimicry. IL-17F inhibited tumour angiogenesis in three cancer types: liver [85], colon [20], and oral [21,84]. IL-17F inhibited oral carcinoma cell proliferation, random cell migration and vasculogenic mimicry [21,84], controlled the cell cycle through p27 and p38, and diminished oxidative stress-causing G2/M phase arrest in colon carcinoma cells [82].

Mechanisms for protumorigenic effects of IL-17F
In addition to the possible macrophage-mediated, proangiogenic role of IL-17F presented by Ferreira et al. [86], IL-17F was found to contain also other protumorigenic properties, through inflammation [83], epithelialmesenchymal transition [15] NFkB regulation [24] and MAPK/ERK activation [81]. Zhou et al. [83] showed that IL-17F might enhance inflammatory processes in inflammation-associated cancer through activation of p65 NFkB. Similarly, Sherry et al. [24] reported that IL-17F causes NFkB phosphorylation in T-and B-cells of CLC patients.  Conditioned media from IL-17F-stimulated macrophages promoted lung cancer progression by enhancing cancer cell migration in vitro and tumour growth in vivo [86], but no connection existed between IL-17F and lung tumour number in a mouse model [87], nor was there any connection between lung cancer cell viability and glycolytic metabolism in vitro [86].
The CRC cell migration and invasion promoting role of IL-17F was caused by induction of epithelialmesenchymal transition of HCT-116 cells [15]. Similarly, Chen et al. [81] found that IL-17F enhances MCF-7, a breast cancer cell line, cell proliferation, migration and invasion via activation of the MAPK/ERK signaling pathway. In Apc Min/+ mice, knockout of IL-17F inhibited Abbrevations: AML = acute myeloid leukemia, BCC = basal cell carcinoma, CIHM = CpG island hypermethylation, CRC = colorectal cancer, HBV = hepatitis B virus, HCC = hepatocellular carcinoma, LARC = locally Advanced Rectal Cancer, OS = overall survival, OSCC = oral squamous cell carcinoma, PFS = progression-free survival small intestine tumorigenesis, and this was associated with decreased IL-1b, Cox-2, and IL-17RC expression [88]. In addition, IL-17F was not associated with a TILderived proliferative effect in CRC [89].

Discussion
In this systematic review, we aimed to clarify the role of IL-17F, protein and mRNA expression and polymorphisms, in cancer and the mechanisms through which IL-17F affects cancer development and progression. We collected publications from four databases (Ovid Medline, PubMed, Scopus, and Cochrane Library). Based on the collected data, IL-17F seems to play a role in cancer development and progression. However, this role was shown to be either pro-or antitumorigenic depending on the cancer type, the source (tissue or fluid) from which it was measured, and the form (protein or mRNA) in which it was analyzed. The correlation between IL-17F polymorphism and cancer incidence or patients' prognosis seemed to be weak in every cancer analyzed. Effects of IL-17F on cancer progression were shown to be through several different mechanisms. Chen et al. 2020 [81] Colorectal in vitro HCT116 cells IL-17F promotes cancer cell migration and invasion by inducing epithelial-mesenchymal transition Chen et al., 2019 [15] in vitro HCT116 wild-type and IL-17F overexpressing cell clones IL-17F plays an important role in colon cancer development through regulation of cell cycle. This could partially happen through IL-17F effects on p27 and p38.
Tong et al. 2014 [82] in Ferreira et al. 2020 [86] in vivo CCSP cre /K-ras G12D mice IL-17F has no effect on lung cancer development in Kras mutated mouse model. The correlation between IL-17F expression and cancer has been studied in 13 different cancers in 34 publications. The results have varied in different cancers and depending on the expression (protein or mRNA) and location (tumour tissue or soluble) of IL-17F. The main findings concerning IL-17F protein expression were in OSCC, which showed that IL-17F expression in tumor tissue and patient serum, but not in saliva, was associated with better prognosis [22,23,44,45]. The opposite effect was noticed in prostate cancer [40,41]. In the case of colorectal cancer and lymphomas, which were studied quite extensively, the results were inconclusive [15-20, 31-36, 43]. In other cancers, there were only a few studies or the results varied too much to draw a clear conclusion. This variation in the role of IL-17F in different cancers is common also in other proteins such as MMP-8 [90]. Despite IL-17A and IL-17F binding to the same receptors, namely IL-17RA and IL-17RC, and sharing high homology, IL-17A has a clearer protumorigenic effect [9], while the role of IL-17F is variable. One clear example of the variation between the two cytokines is their role in oral cancer. As mentioned earlier, IL-17F was shown to be an antitumour cytokine in most of the analysed articles in this review, while IL-17A was reported more than once to be a protumour cytokine [91,92].
The association between IL-17F polymorphisms and cancer was another important aspect in this review, but again the results were variable. Rs763780 polymorphisms have been broadly studied in CRC and gastric cancers [17, 19, 53-61, 63-66, 68, 75], but the findings have been diverse. Other IL-17F SNPs has been less extensively analyzed, and more studies are needed to confirm the relevance of IL-17F polymorphisms in various cancers. As with the expression results, the data for IL-17A polymorphisms are more solid than for IL-17F. The results of a meta-analysis covering 10 case-control studies, involving 4516 cases and 5645 controls, showed a significant association between IL-17A polymorphisms and the risk of developing cancer, particularly gastric cancer, in the Asian (and Chinese) population [93].
There were only a few functional studies of IL-17F, suggesting both an anti-and protumorigenic roles. One of the main mechanisms by which IL-17F exerts its antitumorigenic effect is the inhibition of angiogenesis and vasculogenic mimicry, which was reported in four studies [20,21,84,85]. Inhibition of tumour angiogenesis and vasculogenic mimicry could thus be a potential therapeutic target in cancer treatment [94]. Other antitumorigenic mechanisms of IL-17F included the inhibition of cancer cell proliferation and migration [21] and cell cycle regulation [82]. A protumorigenic role of IL-17F could be caused by regulation of inflammatory responses [83], epithelial-mesenchymal transition [15], IL-1b, Cox-2, and IL-17CR expression [88] and MAPK/ERK activation [81]. Since Ferreira et al. [86] assessed the effects of IL-17A and IL-17F simultaneously, their findings cannot be extrapolated to IL-17F alone. In our search for the functional studies of IL-17F in cancer, we detected two interesting articles reporting opposite results about the role of IL-17F in colon cancer. Tong and his colleagues claimed an anti-tumorigenic role for IL-17F by showing a significant decrease in the tumor growth when IL-17F over expressed HCT116 cells transplanted subcutaneously in nude mice comparing with the mock transfectants [20]. They also used AOM-DSS induced inflammation-associated colon cancer IL-17F −/− mice model to show that these mice had higher colonic tumor numbers and tumor areas compared with the wild-type controls. After further analysis, they found that this antitumorgenic role in both models was possibly a result of inhibition of tumor angiogenesis through decreasing VEGF levels and CD31 + cells. On the other hand, Chae and Bothwell used Apc Min/+ mice model highly susceptible to develop spontaneous intestinal adenoma to study the effect of IL-17F on intestinal cancer [88]. Opposite to the Tong et al., IL-17F knockout Apc Min/+ mice inhibited the spontaneous intestinal tumorigenesis compared with the Apc Min/+ mice. This was also associated with reducing IL-1β, Cox-2, and IL-17RC expression suggesting proinflammatory and protumorgenic roles of IL-17F in intestinal cancer [88]. These contrary results are confusing, however they could be due to the different mice models used in the two studies.
In contrast to IL-17A, which has already been studied intensively, IL-17F has thus far received much less attention in the cancer research field. Based on our criteria, only 79 articles were included in this review, which is a low number considering that we included all types of cancer. Weaknesses of this review comprise its broad scope and the large number of different types of studies, making it impossible to provide an in-depth analysis of them. Additionally, studies included in this article examined a variety of different designs, study populations and primary/secondary outcomes, which unfortunately reduce the value of direct interstudy comparisons and therefore these comparisons should be taken with caution. Nevertheless, this review gives an overall picture of the variable IL-17F roles in different cancers.
In conclusion, more well-designed studies of IL-17F are needed to elucidate its molecular mechanisms in different types of cancer. These studies are important to address several aspects such as the difference in the function between tissue or soluble IL-17F, the affected pathways through which IL-17F exert its effect, the effect of IL-17F on the tumor stroma cells, especially inflammatory cells, and if targeting IL-17F could provide a therapeutic benefits for cancer patients.