Identification of FIP200 interaction with the TSC1–TSC2 complex and its role in regulation of cell size control

Abstract

FIP200 (focal adhesion kinase [FAK] family interacting protein of 200 kD) is a newly identified protein that binds to the kinase domain of FAK and inhibits its kinase activity and associated cellular functions. Here, we identify an interaction between FIP200 and the TSC1–TSC2 complex through FIP200 binding to TSC1. We found that association of FIP200 with the TSC1–TSC2 complex correlated with its ability to increase cell size and up-regulate S6 kinase phosphorylation but was not involved in the regulation of cell cycle progression. Conversely, knockdown of endogenous FIP200 by RNA interference reduced S6 kinase phosphorylation and cell size, which required TSC1 but was independent of FAK. Furthermore, overexpression of FIP200 reduced TSC1–TSC2 complex formation, although knockdown of endogenous FIP200 by RNA interference did not affect TSC1–TSC2 complex formation. Lastly, we showed that FIP200 is important in nutrient stimulation-induced, but not energy- or serum-induced, S6 kinase activation. Together, these results suggest a cellular function of FIP200 in the regulation of cell size by interaction with the TSC1–TSC2 complex.

HIF1α and HIF2α: sibling rivalry in hypoxic tumour growth and progression

“…The focal adhesion kinase (FAK) family interacting protein of 200 kd (FIP200) gene has been identified as a HIF2α target through microarray studies 27 and FIP200 has been proposed to interact with TSC1, thereby disrupting TSC1ITSC2 complexes and promoting mTORC1 activation 133 . In addition, FIP200 may promote TSC1 degradation by the ubiquitin-proteosome pathway 134 .…”

Stress and mTORture signaling

“…FIP200 overexpression stimulated S6K activity and disrupted the TSC complex. Cells devoid of FIP200 partially blocked nutrient-stimulated S6K phosphorylation, suggesting that it is required to transduce a nutrient-derived signal to the mTOR complex (Gan et al, 2005). Another unanswered question is why hVps34 activity is inhibited upon amino-acid depletion despite being an important positive regulator of autophagy.…”

FIP200, a key signaling node to coordinately regulate various cellular processes

“…Most studies so far showed that FIP200 is a cytoplasmic protein [3,6,7,11,12]. However, FIP200 has also been shown to localize in focal adhesion [13] and nucleus [8,14].…”

“…So far, totally 8 proteins have been identified as FIP200 interacting proteins, including stathmin [6], Pyk2 [3], FAK [13], ActA [7], p53 [14], TSC1 [11,15], ASK1 and TRAF2 [12] (Table 1). It should be noted that not all FIP200 interacting proteins have been confirmed at the endogenous level and therefore the significance of some interactions should be more rigorously studied.…”

“…Finally, it seems that FIP200 plays very diverse biochemical functions with different binding partners (Table 1). FIP200 functions to directly inhibit FAK and Pyk2 kinase activities [3,13], disrupt TSC1-TSC2 complex formation [11], regulate p53 and TSC1 protein stability [14,15], serve as a scaffolding to facilitate TRAF2-ASK1 signaling to JNK activation [12], and regulate the transcription of Rb1 when localizing in nucleus [4]. Since most of these binding partners associate with different regions of FIP200 (Figure 1), it is possible that FIP200 can exert multiple biochemical functions through different domains.…”