Expression of the Axl receptor tyrosine kinase in human thyroid carcinoma

Coexpression of growth arrest-specific gene 6 and receptor tyrosine kinases Axl and Sky in human uterine endometrial cancers

BACKGROUND

Gas6, the protein product of the growth arrest-specific gene 6 (gas6), a member of the vitamin K-dependent protein family, was identified as a ligand for the Axl/Sky family of receptor tyrosine kinases. Gas6 acts as a growth-potentiating factor for thrombin-induced proliferation of vascular smooth muscle cells. The aim of the present study was to test for the presence of Gas6 and its receptors Axl and Sky, related to specific growth in uterine endometrial cancers, and to evaluate their plausible growth potential and mechanism.

MATERIALS AND METHODS

Sixty patients underwent curative resection for uterine endometrial cancers. In uterine endometrial cancers, the mRNA levels and histoscores of Gas6, Axl and Sky were determined by competitive RT-PCR using recombinant RNA and immunohistochemical studies, respectively. The rate of proliferation by immunochemistry for Ki67 and the rate of apoptosis by TUNEL were determined.

RESULTS

The mRNA levels and the histoscores of Gas6 and Axl in well-differentiated endometrial cancers (G1 EC) were significantly higher than in normal uterine endometrium (NE) and in moderately and poorly differentiated endometrial cancers (G2 + G3 EC). The rate of apoptosis in G1 EC was significantly lower than that in NE and in G2 + G3 EC.

CONCLUSIONS

Gas6 and Axl signal transduction is aberrantly stimulated in well-differentiated endometrial cancers, plausibly related to tumor progression due to protection from apoptosis in cancers cells.

Interaction of Axl receptor tyrosine kinase with C1-TEN, a novel C1 domain-containing protein with homology to tensin

Axl receptor tyrosine kinase is implicated in several malignancies and is the receptor for the vitamin K-dependent growth factor Gas6. From a yeast two-hybrid screen of protein-protein interactions with the Axl cytoplasmic domain, we detected a previously uncharacterised SH2 domain-containing protein. We cloned two novel splice variants of this protein that give rise to 1409- and 1419-amino acid proteins, differing only in their N-terminal residues and yielding a 150-kDa protein product by in vitro translation. The Axl-interacting C-terminus contains a tandem SH2 and PTB domain combination homologous to the focal adhesion protein tensin. We detected interaction of Axl with both domains in mammalian cells by co-immunoprecipitation and two-hybrid analyses. In addition, the protein possesses an N-terminal putative phorbol ester-binding C1 domain as well as a central tyrosine phosphatase motif. Thus, we have named the protein C1 domain-containing phosphatase and TENsin homologue (C1-TEN). Northern blot analysis of C1-TEN in human tissues revealed highest expression in heart, kidney, and liver. In summary, we have identified a novel multi-domain intracellular protein that interacts with Axl and which may furthermore be involved in other signal transduction pathways.

Expression of receptor-type tyrosine kinase, Axl, and its ligand, Gas6, in pediatric thyroid carcinomas around chernobyl

Protein-tyrosine kinases (PTKs) play a crucial role in regulating thyroid cell growth and differentiation. It is known that PTKs are activated by ionizing radiation, but the critical pathways through ionizing radiation-induced malignant transformation are not well defined. The Axl protein is a member of a new family of receptor tyrosine kinases, which the ligand, Gas6, a protein S-related molecule, has recently been identified. We previously clarified the expression of Axl and mitogenic action of Gas6 in thyroid carcinoma cells. To investigate the involvement of Gas6-Axl signaling in pediatric thyroid carcinoma further, we examined tissues obtained from 17 patients with thyroid papillary carcinomas from Gomel, Belarus, by immunohistochemistry and in situ hybridization. Axl and Gas6 were overexpressed in 76.5% and 70.6 % of cases, respectively. Solid component and invasive front tended to overexppress Gas6 and Axl in papillary carcinomas. Eighty-five percent of Axl positive cases coexpressed Gas6. In situ hybridization also confirmed the presence of axl mRNA in thyroid carcinoma tissues. These findings suggest that Axl and Gas6 expression might be involved in childhood thyroid tumorigenesis around Chernobyl.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.