HSH2: a novel SH2 domain-containing adapter protein involved in tyrosine kinase signaling in hematopoietic cells.

We isolated a cDNA clone encoding a novel Src homology (SH)2 domain-containing protein of 47 kDa from a human cDNA library. As its transcript was predominantly expressed in hematopoietic cells, this gene was termed HSH2 for hematopoietic SH2 protein. This protein contains several putative protein-binding motifs, SH3-binding proline-rich regions, and phosphotyrosine sites, but lacks enzymatic motifs. In a yeast two-hybrid screen, we identified a cytokine-regulated tyrosine kinase c-FES and an activated Cdc42-associated tyrosine kinase ACK1 as HSH2 interactors. HSH2 bound c-FES via its C-terminal region as well as its N-terminal region including the SH2 domain, whereas it bound ACK1 via its N-terminal proline-rich region. Furthermore, these two kinases bound and tyrosine-phosphorylated HSH2 in mammalian cells. Hence, we postulate that HSH2 functions as an adapter protein involved in tyrosine kinase signaling, and possibly regulates cytokine signaling and cytoskeletal reorganization, in hematopoietic cells.

Regulatory mechanism of Ca2+/calmodulin-dependent protein kinase kinase.

Ca(2+)/calmodulin-dependent protein kinase kinase (CaM-KK) is a novel member of the CaM kinase family, which specifically phosphorylates and activates CaM kinase I and IV. In this study, we characterized the CaM-binding peptide of alphaCaM-KK (residues 438-463), which suppressed the activity of constitutively active CaM-KK (84-434) in the absence of Ca(2+)/CaM but competitively with ATP. Truncation and site-directed mutagenesis of the CaM-binding region in CaM-KK reveal that Ile(441) is essential for autoinhibition of CaM-KK. Furthermore, CaM-KK chimera mutants containing the CaM-binding sequence of either myosin light chain kinases or CaM kinase II located C-terminal of Leu(440), exhibited enhanced Ca(2+)/CaM-independent activity (60% of total activity). Although the CaM-binding domains of myosin light chain kinases and CaM kinase II bind to the N- and C-terminal domains of CaM in the opposite orientation to CaM-KK (Osawa, M., Tokumitsu, H., Swindells, M. B., Kurihara, H., Orita, M., Shibanuma, T., Furuya, T., and Ikura, M. (1999) Nat. Struct. Biol. 6, 819-824), the chimeric CaM-KKs containing Ile(441) remained Ca(2+)/CaM-dependent. This result demonstrates that the orientation of the CaM binding is not critical for relief of CaM-KK autoinhibition. However, the requirement of Ile(441) for autoinhibition, which is located at the -3 position from the N-terminal anchoring residue (Trp(444)) to CaM, accounts for the opposite orientation of CaM binding of CaM-KK compared with other CaM kinases.

A novel TATA-binding protein-binding protein, ABT1, activates basal transcription and has a yeast homolog that is essential for growth.

Identification of a novel mouse nuclear protein termed activator of basal transcription 1 (mABT1) that associates with the TATA-binding protein (TBP) and enhances basal transcription activity of class II promoters is described. We also identify mABT1 homologous counterparts in Caenorhabditis elegans and Saccharomyces cerevisiae and show the homologous yeast gene to be essential for growth. The mABT1 associated with TBP in HeLa nuclear extracts and with purified mouse TBP in vitro. In addition, ectopically expressed mABT1 was coimmunoprecipitated with endogenous TBP in transfected cells. More importantly, mABT1 significantly enhanced transcription from an adenovirus major late promoter in a reconstituted cell-free system. We furthermore demonstrate that mABT1 consistently enhanced transcription from a reporter gene with a minimal core promoter as well as from reporter genes with various enhancer elements in a cotransfection assay. Taken together, these results suggest that mABT1 is a novel TBP-binding protein which can function as a basal transcription activator.

cDNA cloning and expression analysis of mouse zf9, a Krüppel-like transcription factor gene that is induced by adipogenic hormonal stimulation in 3T3-L1 cells.

Using a differential hybridization method, we have cloned a zinc finger transcription factor gene whose expression was enhanced by adipogenic hormones in preadipocyte 3T3-L1 cells. Cloning of this gene revealed that it encodes a mouse homologue of rat Zf9 and human CPBP/GBF, previously identified as a wound-induced transcription factor and GC-rich binding protein, respectively. The mRNA for this clone consisted of 0.9 kb coding region and 3.2 kb long 3' untranslated region. Northern blot analysis revealed that it was ubiquitously expressed, among adult tissues, in which abundant expression was observed in lung, ovary and thymus. The transcript was transiently induced by different stimuli such as serum, cAMP and 12-O-tetradecanoylphorbol 13-acetate. Nuclear run-on and RNA synthesis inhibitor chase experiments indicated that the transient induction of the mRNA was regulated both at transcriptional and post-transcriptional levels.

Ca(2+)/Calmodulin-dependent protein kinase cascade in Caenorhabditis elegans. Implication in transcriptional activation.

We have recently demonstrated that Caenorhabditis elegans Ca(2+)/calmodulin-dependent protein kinase kinase (CeCaM-KK) can activate mammalian CaM-kinase IV in vitro (Tokumitsu, H., Takahashi, N., Eto, K., Yano, S., Soderling, T.R., and Muramatsu, M. (1999) J. Biol. Chem. 274, 15803-15810). In the present study, we have identified and cloned a target CaM-kinase for CaM-KK in C. elegans, CeCaM-kinase I (CeCaM-KI), which has approximately 60% identity to mammalian CaM-KI. CeCaM-KI has 348 amino acid residues with an apparent molecular mass of 40 kDa, which is activated by CeCaM-KK through phosphorylation of Thr(179) in a Ca(2+)/CaM-dependent manner, resulting in a 30-fold decrease in the K(m) of CeCaM-KI for its peptide substrate. Unlike mammalian CaM-KI, CeCaM-KI is mainly localized in the nucleus of transfected cells because the NH(2)-terminal six residues ((2)PLFKRR(7)) contain a functional nuclear localization signal. We have also demonstrated that CeCaM-KK and CeCaM-KI reconstituted a signaling pathway that mediates Ca(2+)-dependent phosphorylation of cAMP response element-binding protein (CREB) and CRE-dependent transcriptional activation in transfected cells, consistent with nuclear localization of CeCaM-KI. These results suggest that the CaM-KK/CaM-KI cascade is conserved in C. elegans and is functionally operated both in vitro and in intact cells, and it may be involved in Ca(2+)-dependent nuclear events such as transcriptional activation through phosphorylation of CREB.

Cloning and expression profile of mouse and human genes, Rnf11/RNF11, encoding a novel RING-H2 finger protein.

The RING finger (C3HC4-type zinc finger) is a variant zinc finger motif presents in a new family of proteins. A new member of the RING finger family was identified and its cDNA structures were determined in human and mouse. The predicted protein consisting of a 144 amino acid residues is very conservative between the two species and contains a canonical RING-H2 finger motif (C3H2C2) at the carboxyl-terminal region. The genes were designated as RNF11/Rnf11 for RING finger protein 11. A single 2.4-kb transcript of mouse Rnf11 was ubiquitously expressed in various fetal and adult mouse tissues by the Northern blot analysis. The human RNF11 gene was mapped on chromosome 1p31-p32 region, where frequent alterations have been observed in T-cell acute lymphoblastic leukemia.

Transforming growth factor-beta is a survival factor for neonate cortical neurons: coincident expression of type I receptors in developing cerebral cortices.

Transforming growth factor-beta (TGF-beta) is a multifunctional polypeptide which plays a crucial role in the regulation of cell proliferation, differentiation, and organogenesis. In the present study, we investigated the expression of signaling receptors for TGF-beta in developing mice by in situ hybridization, revealing a significant difference in the expression of TGF-beta type I and type II receptors. Unexpectedly, the TGF-beta type I receptors were exclusively expressed without any detectable expression of the TGF-beta type II receptors in developing cerebral cortices. In primary cortical neurons, a neutralizing antibody for TGF-beta significantly reduced the expression of bcl-2 and subsequently induced neuronal cell death, indicating that TGF-beta functions as a survival factor for cortical neurons in vitro. Consistent with the result of in situ hybridization, the TGF-beta, type I but not type II receptors were detected in primary cortical neurons by affinity crosslink and RT-PCR analyses. The concomitant expression of TGF-beta2 and the TGF-beta type I receptors in developing cerebral cortices suggests that the TGF-beta signaling system plays a pivotal role in neuronal differentiation and that unidentified components may be involved in TGF-beta signaling in the development of the central nervous system.