Eugene Medlock

Noninsulin-dependent diabetes mellitus occurs in mice ectopically expressing the human Axl tyrosine kinase receptor.

The axl tyrosine kinase receptor is aberrantly expressed on myeloid cells of many individuals afflicted with chronic myelogenous leukemia (CML) and other myeloid leukemias. Although previous studies demonstrated this kinase to have oncogenic potential, it is not known whether axl actively participates in the onset and/or progression of CML. We addressed this question by generating transgenic mice possessing constitutive ectopic expression of human axl throughout cells of the myeloid hematopoietic lineage through the use of the granulocyte colony‐stimulating factor (GCSF) receptor promoter. The transgenics did not exhibit hematopoietic malignancies, but did exhibit phenotypic characteristics associated with noninsulin‐dependent diabetes mellitus (NIDDM) including hyperglycemia and hyperinsulinemia, severe insulin resistance, progressive obesity, hepatic lipidosis, and pancreatic islet dysplasia. The obese‐diabetes phenotype was similar to that observed in the agouti and melanocortin‐4−/− mutants, however the axl transgenics were not hyperphagic. Axl transgenic animals expressed elevated serum tumor necrosis factor (TNF)‐alpha levels that were further enhanced upon in vitro lipopolysaccharide (LPS) stimulation of peripheral blood. Administration of the axl ligand, gas6, to peripheral transgenic blood samples eliminated excessive TNF‐alpha production in response to LPS stimulation. As a means to better understand axl‐gas6 biology, transgenic animals were produced which systemically expressed the gas6‐binding axl proteolytic cleavage product. A more severe NIDDM phenotype occurred in these mice. The observed phenotypes may be related to the axl receptor or proteolytic cleavage product competing with related axl family receptors for binding of the gas6 ligand. We conclude that axl expression in myeloid cells in itself does not lead to the onset or progression of leukemia and suggest that ectopic axl expression affects endogenous modulation of TNF‐alpha production indirectly resulting in the NIDDM phenotype. J. Cell. Physiol. 181:433–447, 1999.

Protein tyrosine phosphatase (PC12, Br7,Sl) family: Expression characterization in the adult human and mouse

Protein tyrosine phosphatases (PTPs) play important roles in modulating signals transduced by tyrosine kinases. Certain phosphatases have been implicated as having important roles in embryonic development as well as in adult physiology. Although both kinases and phosphatases are equally important in regulating signal transduction, phosphatases as a group have not been well characterized. Thus, characterization of sequence, expression, and biological function for additional phosphatases is informative. PTPBr7/PC12 and PTPSl are mouse receptor PTPs sharing similar amino acid sequences. Northern blot analysis demonstrated expression of these genes in adult rodent brain and revealed previously uncharacterized transcripts in the brain and other tissues. Our results demonstrate that PTPBr7/PC12 and PTPSl are members of a larger family of PTPs. We have identified two novel family members as well as several novel transcriptional splice variants from both human and mouse colon cDNA libraries. Expression analysis demonstrated that the various mRNA transcripts are differentially expressed, with the highest levels found in the brain, intestinal tract, uterus, and placenta. In situ hybridization analysis of mouse brain and intestinal tissues established that each isoform has a unique expression pattern in specific cell populations as well as in tissue regions. Furthermore, these restricted patterns suggest that the encoded family of phosphatases may play roles in modulating signal transduction pathways important for specific cell types and biological processes. Anat Rec 258:221–234, 2000.

Involvement of CSF-1 in generating a stroma-independent hematopoietic stem cell line†

The hematopoietic stem cell line, Myl‐D7, is maintained by a self‐renewing stem cell population that spontaneously generates myeloid, lymphoid, and erythroid progeny. MS‐5 stromal cells are necessary for the growth of Myl‐D7 cells. One component of the Myl‐D7 cells proliferation activity released by MS‐5 stromal cells was enriched by Q sepharose fractionation and shown to be colony stimulating factor‐1 (CSF‐1) by Western blotting, BAC1.2F5 cell bioassay and inhibition of Myl‐D7 proliferation by CSF‐1 antibody. The requirement of Myl‐D7 cells for CSF‐1 was also demonstrated independently by selecting for rare, stroma‐independent Myl‐D7 mutant clones able to grow without stroma and additional factors. Eighty‐nine stroma‐independent mutant clones were obtained and belonged to two classes. The majority of mutants did not secrete any growth promoting activity. The second, rarer class of mutants releases a factor that stimulates proliferation/survival for up to several months and approximately half of the secretors express high levels of CSF‐1 mRNA. Wild type Myl‐D7 grown with supernatants from the secretor cells retained the stem cell phenotype. These data suggest that CSF‐1 may act as a key factor in stroma‐regulated hematopoiesis and cell–cell interaction. J. Cell. Physiol. 206: 556–562, 2006.