Identification of sirm, a Novel Insulin-regulated SH3 Binding Protein That Associates with Grb-2 and FYN

Abstract

We have previously developed a mouse model of insulin-resistant diabetes by targeted inactivation of the insulin receptor gene. During studies of gene expression in livers of insulin receptor-deficient mice, we identified a novel cDNA, which we have termed sirm (Son of Insulin Receptor Mutant mice). sirm is largely, albeit not exclusively, expressed in insulin-responsive tissues. Insulin is a potent modulator of sirm expression, and sirm mRNA levels correlate with tissue sensitivity to insulin. The product of the sirm gene is a serine/threonine-rich protein with several proline-rich motifs and an NPNY motif, conforming to the consensus sequence recognized by the phosphotyrosine binding domains of insulin receptor substrate and Shc proteins. However, Sirm bears no extended homologies with other known proteins. Based on the sequences of the proline-rich domains, we sought to determine whether Sirm binds to the SH3 domains of FYN and Grb-2. We demonstrate here that Sirm binds to FYN and Grb-2 in 3T3-L1 adipocytes and that insulin treatment results in the dissociation of the Sirm⅐FYN and Sirm⅐Grb-2 complexes. We also show that Sirm is a substrate for the kinase activity of FYN in vitro. Based on the patterns of expression of sirm, its regulation by insulin, and the interactions with molecules in the insulin signaling pathway, we surmise that Sirm plays a role in modulating tissue sensitivity to insulin.

Insulin Stimulates Phosphorylation of the Forkhead Transcription Factor FKHR on Serine 253 through a Wortmannin-sensitive Pathway

“…mRNA was isolated by acid phenol-guanidinium extraction, followed by affinity chromatography on oligo(dT). Northern blotting was performed as described (23). The FKHR (nucleotides 1468 -1963) and FKHRL1 (nucleotides 603-2866) probes were obtained by reverse PCR using mouse liver as an RNA source.…”

Severe muscle wasting and denervation in mice lacking the RNA-binding protein ZFP106

“…These neurodegenerative diseases are genetically heterogeneous, with mutations in proteins associated with diverse cellular and molecular functions (7)(8)(9)(10). Although the precise disease mechanisms underlying the pathogenesis of these disorders remain unclear, abnormalities in apoptotic signaling, oxidative stress, protein folding, and RNA processing in motor neurons and skeletal muscle have been implicated in these diseases (11)(12)(13)(14)(15).In a bioinformatics screen for nuclear proteins with enriched expression in skeletal muscle, we identified ZFP106, a zinc finger protein first characterized as an immunodominant cytotoxic determinant of the mouse H3 minor histocompatibility complex (16,17). Zinc fingers (ZnFs) mediate DNA, RNA, and protein interactions and are commonly found in regulatory proteins that govern gene transcription, translation, RNA trafficking, and splicing (18).…”

“…In a bioinformatics screen for nuclear proteins with enriched expression in skeletal muscle, we identified ZFP106, a zinc finger protein first characterized as an immunodominant cytotoxic determinant of the mouse H3 minor histocompatibility complex (16,17). Zinc fingers (ZnFs) mediate DNA, RNA, and protein interactions and are commonly found in regulatory proteins that govern gene transcription, translation, RNA trafficking, and splicing (18).…”

“…ZFP106 is annotated as a multizinc finger and WD40 repeat-containing protein that localizes to the nucleus. A number of cellular functions have been proposed for ZFP106, such as signaling from the insulin receptor, regulation of rRNA transcription, nucleosome assembly through interaction with the testis-specific nucleolar protein TSG118 (Knop1) and the Y-encoded-like protein (TSPYL), and testis development (17,19,20). The necessity of ZFP106 for motor and sensory neuronal maintenance and survival has recently been described (21); however, the molecular role of ZFP106 required for maintaining normal nerve-muscle signaling remains unclear.…”

Cloning and Expression of a Novel Nuclear Matrix-associated Protein That Is Regulated during the Retinoic Acid-induced Neuronal Differentiation

“…Another interesting feature is the proline-rich motif, conforming to the SH3-binding consensus PXXP (27). The sequence TLPLPLRP shares high homology with the proline-rich domain of yet another serine/ threonine-rich protein, Sirm (28). In addition, Ramp contains an LXXLL motif.…”