Reduced cell adhesion during mitosis by threonine phosphorylation of β1 integrin

Abstract

Cell shape and adhesion of cultured mammalian cells change dramatically during mitosis, however, how cell cycle-dependent alterations in cell adhesion are regulated remain to be elucidated. We show here that normal human mammary epithelial (HME) cells which became less adhesive and adopted the rounded morphology during the G(2)/M phase of the cell cycle significantly reduced their dependence on beta1 integrin-mediated adhesion to laminin, by using function blocking antibody to beta1 integrin. In G(2)/M cells, both total and cell surface expressions of beta1 integrin were comparable with those in G(1) cells but it was phosphorylated at threonines 788-789 within its cytoplasmic domain and coimmunoprecipitated Ca(2+)/calmodulin-dependent protein kinase (CaMK) II. The threonine phosphorylated beta1 integrin significantly reduced its intracellular linkage with actin, with no significant reduction in the actin expression. In contrast, beta1 integrin in G(1) cells was not threonine phosphorylated but formed a link with actin and coimmunoprecipitated the core enzyme of the serine/threonine protein phosphatase (PP) 2A. The results suggest that reduced beta1 integrin-mediated cell adhesion of HME cells to the substratum during mitosis may be induced by beta1 integrin phosphorylation at threonines 788-789 and its reduced ability to link with the actin cytoskeleton.

Regulation of protein phosphatase 2A‐mediated recruitment of IQGAP1 to β1 integrin by EGF through activation of Ca2+/calmodulin‐dependent protein kinase II

“…The dissociation of PP2A-IQGAP1 from b1 integrin is accompanied by reduced cell surface expression of b1 integrin in MCF-7 cells (Suzuki and Takahashi, 1999). However, flow cytometric analysis in this study indicates that expression of b1 integrin on the HME cell surface is not reduced by EGF, as in mitotic HME cells (Suzuki and Takahashi, 2003a).…”

Proteomics Analysis Identifies Molecular Targets Related to Diabetes Mellitus-associated Bladder Dysfunction

“…matrix proteins laminin ␥1, nidogen, procollagens (in different isoforms; Table II), and protein phosphatase 2 (Ppp2r1a) are all down-regulated in STZ-induced diabetic rat models. Most of these proteins are known to regulate the very complex and dynamic processes of cell adhesion and migration (41)(42)(43). Four of these proteins are involved in the integrin-mediated cell adhesion pathway (Fig.…”

Specific Phosphorylations Transmit Signals from Leukocyte β2 to β1 Integrins and Regulate Adhesion

“…The phosphorylation of ␤ 1 on Thr-788/ 789 corresponds to the phosphorylation triplet in ␤ 2 , including Thr-758. This phosphorylation reduces ␤ 1 association with the actin cytoskeleton (38) and increases pressure-induced cell adhesion in cancer cells (39). Importantly, cells expressing the activated form of LFA-1 showed reduced phosphorylation of ␤ 1 Thr-788/789.…”