Laminin-5 and modulation of keratin cytoskeleton arrangement in FG pancreatic carcinoma cells: Involvement of IFAP300 and evidence that laminin-5/cell interactions correlate with a dephosphorylation of α6A integrin
✍ Scribed by Baker, Scott E. ;Skalli, Omar ;Goldman, Robert D. ;Jones, Jonathan C.R.
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 625 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0886-1544
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✦ Synopsis
Under normal culture conditions, epithelial cells of the FG line, derived from a pancreatic tumor, characteristically grow in mounds and fail to flatten efficiently onto their substrate. In such cells, keratin intermediate filaments (IFs) are concentrated in the perinuclear region. Furthermore, the IF associated protein, IFAP300, primarily localizes along these keratin bundles. Additionally, a6b4 integrin heterodimers localize in streaks or spots towards the edges of cells while a3b1 integrin is predominantly at cell-cell surfaces. Neither show any obvious interaction with IF. Remarkably, upon plating FG cells into medium containing soluble rat laminin-5, FG cells rapidly adhere and spread onto their substrate. Moreover, FG cells ''capture'' rat laminin-5 and place it basally in circles or arcs at areas of cell-substrate interaction. Double label immunofluorescence microscopy reveals colocalization of IFAP300 as well as a6b4 and a3b1 integrin with the polarized laminin-5. Concomitantly, a6 integrin undergoes dephosphorylation on serine residue 1041. Laminin-5-induced rapid adhesion can be blocked by antibodies against the a3 integrin subunit. In contrast, while a6 integrin antibodies do not block laminin-5-induced rapid adhesion, they prevent FG cells from assuming an epithelial-like morphology. Keratin IF bundles associate with IFAP300-a6b4/a3b1 integrin complexes along the cell-substratum-attached surface of FG cells coincubated in laminin-5-containing medium. Coprecipitation results suggest that in these complexes, IFAP300 may associate with the a6b4 integrin heterodimer. Based on our results and published evidence that IFAP300 binds keratin in vitro J. Cell Biol. 125:159-170], we propose that laminin-5/FG cell interaction results in a novel integrin dephosphorylation event, which subsequently induces IFAP300 association with a6b4 integrin. IFAP300 then mediates the interaction of IFs with the cell surface via the a6b4 integrin heterodimer.