FAK regulates tyrosine phosphorylation of CAS, paxillin, and PYK2 in cells expressing v‐Src, but is not a critical determinant of v‐Src transformation

Abstract

FAK (focal adhesion kinase) is a nonreceptor protein-tyrosine kinase activated by tyrosine phosphorylation following integrin-mediated cell adhesion. Oncogenic Src promotes enhanced and deregulated FAK tyrosine phosphorylation which has been proposed to contribute to altered cell growth and/or morphological properties associated with transformation. In this study, an inducible FAK expression system was used to study the potential role of FAK in v-Src transformation. Our results portray FAK as a major v-Src substrate that also plays a role in recruiting v-Src to phosphorylate substrates CAS (Crk-associated substrate) and paxillin. The FAK Tyr-397 autophosphorylation site was necessary for this scaffolding function, but was not required for v-Src to stably interact with and phosphorylate FAK. FAK was also shown to negatively regulate v-Src mediated phosphorylation of the FAK-related kinase PYK2. Despite these effects, FAK does not play an essential role in targeting v-Src to major cellular substrates including CAS and paxillin. Nor is FAK strictly required to achieve the altered morphological and growth characteristics of v-Src transformed cells.

CAS promotes invasiveness of Src-transformed cells

“…Nevertheless, our results indicate that the presence of CAS is not a strict requirement for Src-mediated morphological transformation and anchorage-independent growth. Similar findings that FAK is dispensable for these characteristics (Hauck et al, 2002;Roy et al, 2002;Moissoglu and Gelman, 2003) further downplay a role for adhesion-associated substrates in these aspects of Src transformation, while anchorage-independent growth has been linked to other oncogenic Src-activated pathways including Ras-MAPK, JAK-STAT, and PI3K-mTOR (Martin, 2001;Frame et al, 2002).…”

“…In the case of the activated SrcF mutant, kinase activity may be further enhanced by SH3 domain displacement (Bra´bek et al, 2002) upon binding to the CAS SBD. In addition to the CAS scaffold mechanism, Src family kinases can also be recruited and activated to phosphorylate FAK, CAS, and paxillin through another mechanism involving direct SH2 binding to the FAK Tyr-397 site (Schaller and Parsons, 1995;Ruest et al, 2000;Roy et al, 2002). Paxillin also can act as a positive regulator of FAK and CAS phosphorylation by Src (Hagel et al, 2002).…”

Overexpression of FAK promotes Ras activity through the formation of a FAK/p120RasGAP complex in malignant astrocytoma cells

“…In contrast, we found here that the stable overexpression of the mutant FAK-397F inhibited the anchorage-independent growth of the malignant astrocytoma cells, and did not result in p120RasGAP association with FAK in cells propagated in aggregate suspension. Transient and stable overexpression of mutant FAK-397F in other cell types has been reported (Renshaw et al, 1999;Roy et al, 2002). Stable overexpression of wild-type or mutant FAK (397F) in v-Src-transformed FAKÀ/À fibroblasts did not alter the ability of the cells to grow in soft agar (Roy et al, 2002).…”

Nek3 kinase regulates prolactin-mediated cytoskeletal reorganization and motility of breast cancer cells

“…Moreover, Nek3 siRNA transfectants showed a significant decrease in serine phosphorylation (Figure 5b), implicating Nek3 as a novel kinase in the regulation of paxillin. Both FAK (Ilic et al, 1995;Roy et al, 2002) and JNK (Huang et al, 2003) have been implicated in cell migration and paxillin phosphorylation. However, our analyses have revealed no interaction between FAK and Nek3, and Nek3 overexpression did not increase JNK activity (data not shown).…”