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Differential Regulation of a Novel Variant of the ₆ Integrin, _6p¹

Department of Radiation Oncology, Arizona Cancer Center [T. L. D., F. B., A. E. C.], and the Department of Molecular and Cellular Biology [A. E. C.], University of Arizona, Tucson, Arizona 85724-5024

We have reported previously the existence of an M_r 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 µM puromycin), whereas production of the _6p variant was unaffected. The _6p variant was decreased 60% by actin depolymerization (10 µM 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 M_r 10,000 on enzymatic digestion. Finally, inhibition of serine/threonine phosphatases by either calyculin A (15 nM) or okadaic acid (62 µM) 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.