Differential Regulation of a Novel Variant of the 6 Integrin, 6p 1

We have reported previously the existence of an Mr 70,000 form of the 6 integrin called 6p in a variety of human epithelial cell lines. Four different experimental conditions were used to examine the regulation of 6 and 6p integrin. The production of the 6 integrin was decreased by 45% using a protein translation inhibitor (2.25 M puromycin), whereas production of the 6p variant was unaffected. The 6p variant was decreased 60% by actin depolymerization (10 M cytochalasin D) corresponding to a decrease in its surface expression, whereas 6 integrin production was unaffected. The 6p variant was resistant to endoglycosidase H treatment, whereas the 6 integrin was both sensitive and resistant to endoglycosidase H treatment, indicating retention in the endoplasmic reticulum and processing through the Golgi apparatus. Additionally, digestion by endoglycosidase F demonstrated both 6p and 6 integrin contained NH2-linked glycosylations and both shifted Mr 10,000 on enzymatic digestion. Finally, inhibition of serine/threonine phosphatases by either calyculin A (15 nM) or okadaic acid (62 M) did not affect 6p, whereas the production of 6 integrin was decreased by 50%. These data suggest that the production of the 6p variant is distinct from 6 integrin and may involve a post-translational processing event at the cell surface.