The Major Vault Protein Is a Novel Substrate for the Tyrosine Phosphatase SHP-2 and Scaffold Protein in Epidermal Growth Factor Signaling

Abstract

The catalytic activity of the Src homology 2 (SH2) domain-containing tyrosine phosphatase, SHP-2, is required for virtually all of its signaling effects. Elucidating the molecular mechanisms of SHP-2 signaling, therefore, rests upon the identification of its target substrates. In this report, we have used SHP-2 substratetrapping mutants to identify the major vault protein (MVP) as a putative SHP-2 substrate. MVP is the predominant component of vaults that are cytoplasmic ribonucleoprotein complexes of unknown function. We show that MVP is dephosphorylated by SHP-2 in vitro and it forms an enzyme-substrate complex with SHP-2 in vivo. In response to epidermal growth factor (EGF), SHP-2 associates via its SH2 domains with tyrosyl-phosphorylated MVP. MVP also interacts with the activated form of the extracellular-regulated kinases (Erks) in response to EGF and a constitutive complex between tyrosyl-phosphorylated MVP, SHP-2, and the Erks was detected in MCF-7 breast cancer cells. Using MVP-deficient fibroblasts, we demonstrate that MVP cooperates with Ras for optimal EGF-induced Elk-1 activation and is required for cell survival. We propose that MVP functions as a novel scaffold protein for both SHP-2 and Erk. The regulation of MVP tyrosyl phosphorylation by SHP-2 may play an important role in cell survival signaling.Tyrosyl phosphorylation is a dynamic and reversible posttranslational modification catalyzed by the opposing actions of PTKs 1 and PTPs. The coordinated actions of PTKs and PTPs are crucial for the regulation of a multitude of physiological processes such as cell growth, differentiation, migration, adhesion, immune response, cell survival, and apoptosis. Although there is overwhelming evidence to demonstrate a critical role for PTPs in the regulation of cellular physiology, a detailed molecular understanding of the actions of many of these enzymes remains to be determined. In large part, the lack of a precise molecular basis for how PTPs function has stemmed from the difficult task of identifying their substrates. The SH2 domain-containing PTP, SHP-2, is an ubiquitously expressed PTP that has two SH2 domains at the NH 2 terminus, a PTP domain, and a COOH-terminal tail (1-3). Much evidence derived from genetic studies demonstrates that SHP-2 plays a positive role in transducing signals from receptor PTKs (4). Further evidence in mammalian systems for a positive signaling role for SHP-2 has been obtained from mice containing a targeted deletion within exon 3 of murine SHP-2 that deletes the NH 2 terminus SH2 domain (5). SHP-2 exon 3-deleted mice exhibit embryonic lethality (5). Fibroblasts derived from them are defective for the activation of the MAPKs such as the Erks in response to a number of polypeptide growth factors (5-8). These data, as well as those derived from others (9, 10), place SHP-2 upstream of the Erks, and in some cases upstream of either Ras (11), phosphatidylinositol 3-kinase (8, 12, 13) or the Src family kinases (6,14,15).The ability of SHP-2 to transduce downstream signals in such a d...

Nuclear Localization of PTEN Is Regulated by Ca2+ through a Tyrosil Phosphorylation–Independent Conformational Modification in Major Vault Protein

“…Phosphorylation of MVP is reported to depend on the presence of Mg 2+ (15), and EGF stimulation increases MVP tyrosil phosphorylation (12). Additionally, we have recently found that subcellular localization of PTEN is not regulated by PTEN phosphorylation (14).…”

“…Erk has been shown to be imported to the nucleus by two coexisting mechanisms: passive diffusion and Ran-dependent active transport (22). Interestingly, MVP is reported to interact with phosphorylated p44/42 (Erks) in response to EGF stimulation (12). If MVP is involved in nuclear import of phospho-p44/42 as well, MVP-targeted siRNA should decrease nuclear phosphop44/42.…”

“…MVP reportedly interacts with the C2 domain of PTEN through the EF hand-like motif in a Ca 2+ -dependent manner in HeLa cells (10). Phosphorylation of MVP depends on the presence of Mg 2+ in PC12 cells (15), and epidermal growth factor (EGF) stimulation increases tyrosil phosphorylation of MVP in WI38 cells (12). Therefore, we hypothesized that Ca 2+ , Mg 2+ , and tyrosil phosphorylation of MVP may be playing crucial roles in MVP function, particularly in nuclear import of PTEN.…”

The Immune Signaling Adaptor LAT Contributes to the Neuroanatomical Phenotype of 16p11.2 BP2-BP3 CNVs

“…56 The product of MVP that also genetically interacts with LAT has been postulated to act as a scaffold that modulates MAPK/ERK signaling. 57,58 Evidence is accumulating that it might be involved in the regulation of important cell signaling pathways, including PI3K/AKT, based on the finding that MVP binds several phosphatases and kinases such as PTEN, 59 PTPN11 (tyrosine phosphatase SHP-2), 58 as well as MAPK3 58 itself. The activity of the PI3K was shown to be essential to the signaling capacity of LAT-mediated complexes.…”

A novel model to identify interaction partners of the PTEN tumor suppressor gene in human bladder cancer

“…Most importantly, MVP expression is in many cases a significant and independent predictor of drug response [11]. While no direct function for MVP has been described, reports suggest nuclear translocation of target proteins such as PTEN [12], nuclear exclusion of chemotherapeutic drugs [13] and as a scaffold protein downstream of the EGFR [14]. The PTEN / MVP interaction has been previously observed in a yeast two hybrid system, and co-immunoprecipitations have been performed in human cancer cells [12].…”