Analysis of α6A and α6B integrin subunits in colon cancer cell models. (A) Representative competitive RT-PCR of the α6A and α6B variants in six colon cancer cell lines. (B) Immunoprecipitation of the α6 subunits using the G0H3 antibody from metabolically labeled Caco-2/15 cells and keratinocytes and analyzed on SDS-PAGE under nonreduced (NR) and reduced (R) conditions showing that α6 predominantly associates with the β4 subunit in these cells. Apparent molecular weights are indicated on the left side. The dots indicate the expected sites of β1 subunit migration under both NR and R conditions. (C) Further analysis by competitive RT-PCR for splice variant expression of two intestinal cell lines at different differentiation stages showing up-regulation of the α6B variant upon cell-cycle exit. Caco-2/15: proliferative at sub-confluence (SC) while becoming non-proliferative at post-confluence (PC); HT-29: grown under non-permissive (Glu: glucose) or permissive (Ino: inosine) conditions for differentiation and cell cycle exit. (D, E) The α6A/α6B ratio of transcript (D) and protein (E) levels relative to differentiation of the various intestinal cells. Means ± SEM, n = 3–6. *, **: Statistically significantly different with p < 0.05 and 0.01, respectively, from subconfluent Caco-2/15. Tukey's One Way Analysis of Variance (ANOVA).