Deregulated expression of prostate apoptosis response gene-4 in less differentiated lymphocytes and inverse expressional patterns of par-4 and bcl-2 in acute lymphocytic leukemia

Introduction: Prostate apoptosis response gene-4, known as par-4, is a new proapoptotic factor functionally required but not sufficient for apoptosis. Since there is evidence from prostate cancer cells that par-4 is involved in regulation of bcl-2 we assessed expression of par-4 and bcl-2 in different populations of normal and neoplastic lymphocytes. Materials and methods: Expression of par-4 mRNA and protein in different subpopulations of normal and neoplastic lymphocytes was assessed by reverse transcription polymerase chain reaction and Western blot. Results: Par-4 mRNA was not detectable in lymphocytes of healthy volunteers (n = 10), but was present in the majority of samples of chronic lymphocytic leukemia (n = 30), chronic lymphocytic leukemia/prolymphocytic leukemia (n = 6) and acute lymphocytic leukemia (n = 10). Par-4 protein was expressed unanimously in samples of mononuclear cells from healthy volunteers and patients with CLL, but less frequently in immature lymphocytes, including neoplastic cells of CLL/PLL and ALL. The decreased frequency of par-4 expression in immature subpopulations was confirmed by results on lymphocytic cell lines at various stages of maturation. Comparing the expressional patterns of par-4 and bcl-2 there was an inverse relationship of both proteins in ALL and different lymphocytic cell lines, indicating a functional relationship of par-4 and bcl-2. Conclusions: This study establishes par-4 as a factor expressed in the majority of normal and neoplastic lymphocytic cells, demonstrating a decreased frequency of protein expression in less differentiated lymphocytes and an inverse expressional pattern of par-4 and bcl-2 in lymphocytic cell lines and ALL.