Biomedical subjects

Lijuan Mei

Publications and source records attributed to Lijuan Mei.

4 recordsLinked to original sources

PubMed2006

Srcasm corrects Fyn-induced epidermal hyperplasia by kinase down-regulation.

Src family tyrosine kinases (SFKs) are important regulators of epithelial cell growth and differentiation. Characterization of cellular mechanisms that regulate SFK activity will provide insights into the pathogenesis of diseases associated with increased SFK activity. Keratin 14-Fyn (K14) transgenic mice were derived to characterize the effect of Fyn on epidermal growth and differentiation in vivo. The epidermis of K14-Fyn mice is thickened, manifests prominent scale, and exhibits features consistent with hyperproliferation. Increased epidermal Fyn levels correlate with activation of p44/42 MAP kinases, STAT-3, and PDK-1, key signaling molecules that promote epithelial cell growth. The Src-activating and signaling molecule (Srcasm) is a substrate of SFKs that becomes tyrosine-phosphorylated downstream of the EGF receptor. In vitro, increased Srcasm levels promote activation of endogenous Fyn and keratinocyte differentiation. To study the in vivo effect of Srcasm upon Fyn, double transgenic lines were derived. K14-Fyn/Srcasm transgenic mice did not manifest the hyperproliferative phenotype. In contrast, K14-Fyn/Srcasm-P transgenic mice, which express a nonphosphorylatable Srcasm mutant, maintained the hyperproliferative phenotype. Resolution of the hyperproliferative phenotype correlated with reduced Fyn levels in vivo in three experimental systems: transgenic mice, primary keratinocytes, and cell lines. Biochemical studies revealed that Srcasm-dependent Fyn down-regulation requires Fyn kinase activity, phosphorylation of Srcasm, and the Srcasm GAT domain. Therefore, Srcasm is a novel regulator of Fyn promoting kinase down-regulation in a phosphorylation-dependent manner. Srcasm may act as a molecular "rheostat" for activated SFKs, and cellular levels of Srcasm may be important for regulating epithelial hyperproliferation associated with increased SFK activity.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2004

Srcasm modulates EGF and Src-kinase signaling in keratinocytes.

The Src-activating and signaling molecule (Srcasm) is a recently described activator and substrate of Src-family tyrosine kinases (SFKs). When phosphorylated at specific tyrosines, Srcasm associates with Grb2 and p85, the regulatory subunit of phosphoinositide 3-kinase; however, little is known about the role of Srcasm in cellular signaling. Data presented here demonstrate that epidermal growth factor (EGF) receptor ligands promote the tyrosine phosphorylation of endogenous and adenovirally transduced Srcasm in keratinocytes, and that increased levels of Srcasm activate endogenous SFKs, with a preference for Fyn and Src. In addition, Srcasm potentiates EGF-dependent signals transmitted by SFKs in keratinocytes. Tyrosine phosphorylation of Srcasm is dependent on growth factors and the activity of EGFR and SFKs. Increased Srcasm expression enhances p44/42 mitogen-activated protein kinase activity and Elk-1-dependent transcriptional events. Elevated Srcasm levels inhibit keratinocyte proliferation while promoting specific aspects of keratinocyte differentiation. Lastly, Srcasm levels are decreased in human cutaneous neoplasia. Collectively, these data demonstrate that Srcasm plays a role in linking EGF receptor- and SFK-dependent signaling to differentiation in keratinocytes.

Adaptor Proteins, Signal Transducing↗

PubMed2001

'Srcasm: a novel Src activating and signaling molecule.

The Src family tyrosine kinase, Fyn, can facilitate regulation of cell proliferation and differentiation. Mice with mutations in the fyn gene have defects in the brain, immune system, and epidermal differentiation. To identify molecules that may interact with Fyn in the epidermis, we performed a yeast two-hybrid interaction screen of a murine keratinocyte library. A novel adaptor-like molecule was isolated and termed Srcasm for Src activating and signaling molecule. Murine Srcasm is a 52.7-kDa protein that contains a VHS membrane association domain and a number of tyrosine motifs suggesting that it may be a substrate for Src family kinases and serve as an adaptor protein. Northern blot analysis of murine tissues demonstrates that Srcasm expression is highest in brain and kidney. In situ hybridization analysis reveals that srcasm mRNA is expressed in regions of the epidermis and hair follicle where keratinocyte differentiation occurs. In the brain, srcasm mRNA distribution correlates with that of fyn, with both being highly expressed in the hippocampal and cerebellar Purkinje neurons. Fyn can phosphorylate Srcasm, and association of these molecules relies on cooperative binding between the SH2 and SH3 domains of Fyn and corresponding canonical binding sites in Srcasm. Srcasm is capable of interacting with Grb2 and the regulatory subunit of phosphoinositide 3-kinase, p85, in a phosphorylation-dependent manner. The evidence suggests that Srcasm may help promote Src family kinase signaling in cells.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Site-specific integration of bacteriophage VWB genome into Streptomyces venezuelae and construction of a VWB-based integrative vector.

The temperate bacteriophage VWB integrates into the chromosome of Streptomyces venezuelae ETH14630 via site-specific integration. Following recombination of the VWB attP region with the chromosomal attB sequence, the host-phage junctions attL and attR are formed. Nucleotide sequence analysis of attP, attB, attL and attR revealed a 45 bp common core sequence. In attB this 45 bp sequence consists of the 3' end of a putative tRNA Arg(AGG) gene with a 3'-terminal CCA sequence which is typical for prokaryotic tRNAs. Phage DNA integration restores the putative tRNA Arg(AGG) gene in attL. However, following recombination the CCA sequence is missing as is the case for most Streptomyces tRNA genes described so far. Adjacent to VWB attP, an ORF encoding a 427 aa protein was detected. The C-terminal region of this protein shows high similarity to the conserved C-terminal domain of site-specific recombinases belonging to the integrase family. To prove the functionality of this putative integrase gene (int), an integrative vector pKT02 was constructed. This vector consists of a 2.3 kb HindIII-SphI restriction fragment of VWB DNA containing attP and int cloned in a non-replicative Escherichia coli vector carrying a thiostrepton-resistance (tsr) gene. Integration of pKT02 was obtained after transformation of Streptomyces venezuelae ETH14630 and Streptomyces lividans TK24 protoplasts. This vector will thus be useful for a number of additional Streptomyces species in which a suitable tRNA gene can be functional as integration site.

Amino Acid Sequence↗