Androgens repress Bcl-2 expression via activation of the retinoblastoma (RB) protein in prostate cancer cells.

The oncogene Bcl-2 is upregulated frequently in prostate tumors following androgen ablation therapy, and Bcl-2 overexpression may contribute to the androgen-refractory relapse of the disease. However, the molecular mechanism underlying androgenic regulation of Bcl-2 in prostate cancer cells is understood poorly. In this study, we demonstrated that no androgen response element (ARE) was identified in the androgen-regulated region of the P1 promoter of Bcl-2 gene, whereas, we provided evidence that the androgenic effect is mediated by E2F1 protein through a putative E2F-binding site in the promoter. We further demonstrated that retinoblastoma (RB) protein plays a critical role in androgen regulation of Bcl-2. The phosphorylation levels of RB at serine residues 780 and 795 were decreased in LNCaP cells treated with androgens. Ectopic expression of a constitutively active form of RB inhibited expression of Bcl-2. Knockdown of endogenous RB protein by an Rb small inference RNA (siRNA) induced an increase in Bcl-2 levels. Most importantly, the effect of androgens on Bcl-2 was abolished completely by specific inhibition of RB function with a mutated E1A. Finally, androgen treatment of LNCaP cells upregulated specifically levels of the cyclin-dependent kinase inhibitors (CDKIs) p15INK4B and p27KIP1. Ectopic expression of p15INK4B and/or p27KIP1 inhibited Bcl-2 expression. Knockdown of endogenous p15INK4B or p27KIP1 protein with a pool of siRNAs diminished androgen-induced downregulation of Bcl-2 expression. Therefore, our data indicate that androgens suppress Bcl-2 expression through negatively modulating activities of the E2F site in the Bcl-2 promoter by activating the CDKI-RB axis.

Increased arthritis severity in mice coinfected with Borrelia burgdorferi and Babesia microti.

Increased severity of disease and persistence of symptoms have been recently reported in some patients with simultaneous infection of Borrelia burgdorferi and Babesia microti in the northeastern and northern midwest United States. This study used a murine model to examine whether defined disease conditions such as arthritis and carditis differed in severity in mice infected solely with B. burgdorferi and in mice coinfected with B. microti and B. burgdorferi. C3H.HeJ and BALB/c mice cohorts were coinfected or singly infected and then monitored experimentally for 15 and 30 days after inoculation. Carditis and arthritis was determined by blinded histopathologic evaluation of myocardium and tibiotarsal joints. Cytokine measurements were made on lymph node and spleen supernatants for interferon-gamma, interleukin (IL)-4, IL-10, and IL-13. No differences were observed for C3H.HeJ mice cohorts; however, coinfected BALB/c mice had a significant increase in arthritis severity at day 30. This clinical observation was correlated with a significant reduction in expression of the cytokines IL-10 and IL-13.

Disruption of androgen receptor function inhibits proliferation of androgen-refractory prostate cancer cells.

Prostate cancer cells depend on androgens and the androgen receptor (AR) for survival. However, after androgen ablation therapy, tumors relapse to an androgen-refractory state. To determine whether the androgen receptor is critical for proliferation of androgen-refractory prostate cancer cells, we disrupted the activity of the androgen receptor with an antibody and an AR mRNA hammerhead ribozyme in the following cell lines: LNCaP (androgen-sensitive), LNCaP-Rf and LNCaP-C4 (androgen-refractory), and DU-145 (androgen-insensitive). Microinjection of either antibody or ribozyme inhibited proliferation of androgen-refractory cells. These findings demonstrate that the AR is critical for proliferation of androgen-refractory cells, even in the absence of androgens.