Thy28 partially prevents apoptosis induction following engagement of membrane immunoglobulin in WEHI-231 B lymphoma cells.

Thy28 protein is conserved among plants, bacteria, and mammalian cells. Nuclear Thy28 protein is substantially expressed in testis, liver, and immune cells such as lymphocytes. Lymphocyte apoptosis plays a crucial role in homeostasis and formation of a diverse lymphocyte repertoire. In this study, we examined whether Thy28 affects induction of apoptosis in WEHI-231 B lymphoma cells following engagement of membrane immunoglobulin (mIg). Once they were established, the Thy28-overexpressing WEHI-231 cells showed similar expression levels of IgM and class I major histocompatibility complex (MHC) molecule compared with controls. The Thy28-overexpressing cells were considerably resistant to loss of mitochondrial membrane potential (ΔΨm), caspase-3 activation, and increase in annexin-positive cells upon mIg engagement. These changes were concomitant with an increase in G1 phase associated with upregulation of p27(Kip1). The anti-IgM-induced sustained activation of c-Jun N-terminal kinase (JNK), which was associated with late-phase hydrogen peroxide (H(2)O(2)) production, was partially reduced in the Thy28-expressing cells relative to controls. Taken together, the data suggest that in WEHI-231 B lymphoma cells, Thy28 regulates mIg-mediated apoptotic events through the JNK-H(2)O(2) activation pathway, concomitant with an accumulation of cells in G1 phase associated with upregulation of p27(Kip1) in WEHI-231 B lymphoma cells.

Molecular cloning and characterization of the mouse thymocyte protein gene.

Chicken thymocyte protein (cThy28) has recently been identified and implicated to be involved in apoptosis of avian lymphocytes, while its functional role remains undefined. To elucidate the role of Thy28, we have molecularly cloned the mouse Thy28 (mThy28) cDNA and clarified its genomic organization in the present study. The mThy28 cDNA encodes a 226 amino acid protein, whose sequence is highly conserved among bacteria, yeast and plants as well as vertebrates. Northern blot analysis revealed abundant expression of approximately 1 kb mRNA in testis, liver, brain and kidney with lower levels of the expression in thymus, spleen, heart and stomach. The mThy28 gene spans at least 7 kb of genomic DNA, and contains eight exons and seven introns. The 5'-flanking region of the mThy28 gene does not contain a typical TATA box, but contains a putative CCAAT box and presumably multiple transcription initiation sites. Potential Sp1, GATA-1, -2, -3, AP-1, and p300 binding sites were found in the 5'-flanking region of the mThy28 gene. The gene was mapped to mouse chromosome 9.