Abstract
The α6 integrin subunit (ITGA6) pre-mRNA undergoes alternative splicing to form two splicing variants, named ITGA6A and ITGA6B. In primary human colorectal cancer cells, the levels of both ITGA6 and β4 integrin subunit (ITGB4) subunits of the α6β4 integrin are increased. We previously found that the upregulation of ITGA6 is a direct consequence of the increase of the pro-proliferative ITGA6A variant. However, the mechanisms that control ITGA6 expression and splicing into the ITGA6A variant over ITGA6B in colorectal cancer cells remain poorly understood. Here, we show that the promoter activity of the ITGA6 gene is regulated by MYC. Pharmacological inhibition of MYC activity with the MYC inhibitor (MYCi) 10058-F4 or knockdown of MYC expression by short hairpin RNA (shRNA) both lead to a decrease in ITGA6 and ITGA6A levels in colorectal cancer cells, while overexpression of MYC enhances ITGA6 promoter activity. We also found that MYC inhibition decreases the epithelial splicing regulatory protein 2 (ESRP2) splicing factor at both the mRNA and protein levels. Chromatin immunoprecipitation revealed that the proximal promoter sequences of ITGA6 and ESRP2 were occupied by MYC and actively transcribed in colorectal cancer cells. Furthermore, expression studies in primary colorectal tumors and corresponding resection margins confirmed that the up-regulation of the ITGA6A subunit can be correlated with the increase in MYC and ESRP2. Taken together, our results demonstrate that the proto-oncogene MYC can regulate the promoter activation and splicing of the ITGA6 integrin gene through ESRP2 to favor the production of the pro-proliferative ITGA6A variant in colorectal cancer cells.
Highlights
Integrins are the principal transmembrane receptors responsible for cell–extracellular matrix interactions
It is noteworthy that ITGA6B expression was not modulated modulated in tumors relative to their corresponding resection margins [22]
In Caco-2/15 cells, which undergo undergo a spontaneous switch from the ITGA6A to ITGA6B form after confluence [20], we a spontaneous switch from the ITGA6A to ITGA6B form after confluence [20], we observed a observed a significant correlation with the reduction of MYC during the same period (Figure 1d) significant correlation with the reduction of MYC during the same period (Figure 1d) supporting a supporting a possible link between MYC and ITGA6A expression
Summary
Integrins are the principal transmembrane receptors responsible for cell–extracellular matrix interactions. The α6β4 integrin is a unique integrin, with a β4 subunit (ITGB4) displaying an elaborate cytoplasmic domain of more than 1000 amino acids and the α6 subunit (ITGA6) as its only possible α subunit partner [9] In normal epithelia, this laminin receptor promotes stable epithelial cell adhesion through its participation with hemidesmosomes, complex adherent junctional structures that connect intermediate filaments to the basement membrane [10]. While the ITGA6 subunit can undergo alternative splicing of its exon 25, leading to the formation of two distinct variants, identified as ITGA6A and ITGA6B [16], suggesting a potential variation in downstream signalling depending on the α6β4 form. MYC can directly control both ITGA6 and ESRP2 promoter activities in CRC cells, leading to the overexpression of the pro-proliferative ITGA6A splice variant
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
