Identification and characterization of a novel protein kinase gene prediminently expressed in hematopoietic cells

Abstract

In an attempt to identify kinases that are involved in the signal transduction for cell growth, proliferation, and differentiation, a PCR-based screen for unidentified protein kinases was performed. By the PCR using degenearative primers, a cDNA of a putative kinase (HPK38) was isolated from a human keratinocyte cDNA library. The cDNA for MPK38 (the mouse homolog of HPK38) was also isolated from the murine tetracarcinoma PCC4 cell line using HPK38 cDNA. HPK38 and MPK38 were transcribed as an ~1.5kb mRNA ecoding for a protein 651 amino acids (HPK38) and 643 amino acids (MPK38). The sequence of HPK38/MPK38 showed that it is most closely to the SNF1 serine/threonine kinase family, which includes that SNF1, nim1+, KIN1,and KIN2 kinases. The N-terminal region of HPK38 and MPK38 contains the kinase catalytic domain, which exhibits approximately 60% protein sequence identity with the SNF1 serine/threonine kinase family. K1and K33 clones of HPK38 have the disrupted catalytic domain. mRNA of K1 produced translated products if ~50kDa and ~7-kDa in size in vitro. However mRNA of K3 produced only ~50kDa products. MPK38 mRNA was predominantly expressed in thymus and spleen, but was not detectable in kidney, liver, and muscle in the adult tissues. MPK38 mRNA was apparently expressed n T lineage cells and a macrophage/monocyte cells. In contrast, it was detectable in mast cell line after a longer exposure. Interestingly, the incubation of thymocytes at $37\^circ C$ resulted in the loss of MPK38 transcript, and the transcript was able to be induced by treatment with ConA or PHA, not with PMA and various growth factors such as IL-2, IL-7, TGF-beta, TNA-alpha, and EGF. The restricted expression pattern and induction of MPK38 during T cell activation suggest that MPK38 is a signal transduction molecule involved in thymocyte development. The genomic DNa containing 5`` flanking region of MPK38 was isolated froma mouse luekocyte genomic library. Primer extension identified three maj...