Abstract
Prothymosin alpha (ProT alpha) is a widely distributed acidic protein whose function has been related to cell proliferation. We have analyzed the expression of the rat ProT alpha gene in several proliferative systems: concanavalin A (ConA)/interleukin-2-stimulated thymocytes, ConA-stimulated splenic T-lymphocytes, and hepatocytes proliferating during liver regeneration. In these systems, ProT alpha mRNA was detected in all stages of the cell cycle, with maximal increments (2-4-fold) at the beginning of the S phase. By contrast, the mRNAs for proliferating cell nuclear antigen/cyclin and histone H3, two cell-cycle-regulated proteins, were hardly detected in resting cells but increased notably at the G1/S boundary and in the S phase, respectively. Treatment of T-cells with the calcium ionophore A23187 increased ProT alpha mRNA levels 2.5-fold, whereas phorbol 12-myristate 13-acetate, a protein kinase C activator, had no effect on ProT alpha gene expression. Incubation of ConA-stimulated T-cells with hydroxyurea, a DNA synthesis inhibitor, did not decrease the levels of ProT alpha mRNA, indicating that its expression is independent of DNA synthesis. These findings suggest that ProT alpha is required throughout all the stages of the cell cycle, resembling a constitutively expressed gene rather than one strictly involved in cell proliferation.
Highlights
ProTu has been traditionallyregarded as a regulatory protein of cell immunity
We have found that Prothymosin a (ProTa) mRNA levels are higher in immature proliferating thymocytes andin some kinds of leukemia than in mature lymphocytes, suggesting a possible correlation between ProTa gene expression and cell proliferation and/or differentiatio(n11).Immunological studies using a polyclonal antibody against thymosin-a, the 28amino acid N-terminal fragment of ProTa [1, 2], have shown an association between levels of thymosin immunoreactive peptides(TIP)andthe proliferative status of rat IEC-6 cells, describing maximum T I P levels in the GI phase of the cell cycle [15]
Our results showed that ProTa mRNA wasmoderately increased as cells progressed into the S phase, but was present throughout all stages of the cell cycle
Summary
ProTu has been traditionallyregarded as a regulatory protein of cell immunity. In this sense, ProTa enhances resist-. Clumps were removed by filtering, and the cells washed three times proliferating and resting rat thymocytes.
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