Shabirul Haque

A Cyclooxygenase-2/Prostaglandin E2 Pathway Augments Activation-Induced Cytosine Deaminase Expression within Replicating Human B Cells

Within inflammatory environments, B cells encountering foreign or self-Ag can develop tertiary lymphoid tissue expressing activation-induced cytosine deaminase (AID). Recently, this DNA-modifying enzyme was detected in nonlymphoid cells within several inflamed tissues and strongly implicated in malignant transformation. This study examines whether a cyclooxygenase 2 (COX-2) pathway, often linked to inflammation, influences AID expression in activated B lymphocytes. In this paper, we report that dividing human B cells responding to surrogate C3d-coated Ag, IL-4, and BAFF express AID, as well as COX-2. A progressive increase in AID with each division was paralleled by a division-related increase in a COX-2–linked enzyme, microsomal PGE2 synthase-1, and the PGE2R, EP2. Cells with the greatest expression of AID expressed the highest levels of EP2. Although COX-2 inhibitors diminished both AID expression and IgG class switching, exogenous PGE2 and butaprost, a selective EP2 agonist, augmented AID mRNA/protein and increased the numbers of IgG+ progeny. Despite the latter, the proportion of IgG+ cells within viable progeny generally declined with PGE2 supplementation. This was not due to PGE2-promoted differentiation to plasma cells or to greater downstream switching. Rather, because phosphorylated ataxia telangiectasia mutated levels were increased in progeny of PGE2-supplemented cultures, it appears more likely that PGE2 facilitates AID-dependent DNA double-strand breaks that block B cell cycle progression or promote activation-induced cell death, or both. Taken together, the results suggest that a PGE2 feed-forward mechanism for augmenting COX-2 pathway proteins promotes progressively increased levels of AID mRNA, protein, and function.

Renin angiotensin system modulates mTOR pathway through AT2R in HIVAN

Mammalian target of rapamycin (mTOR) has been reported to contribute to the development of HIV-associated nephropathy (HIVAN). We hypothesized that HIV may be activating renal tissue mTOR pathway through renin angiotensin system (RAS) via Angiotensin Receptor Type II receptor (AT2R). Renal tissues of Vpr transgenic and Tg26 (HIVAN) mice displayed enhanced phosphorylation of mTOR and p70S6K. Aliskiren, a renin inhibitor attenuated phosphorylation of both mTOR and p70S6K in renal tissues of HIVAN mice. Interestingly, Angiotensin Receptor Type I (AT1R) blockade did not modulate renal tissue phosphorylation of mTOR in HIVAN mice; on the other hand, AT2R blockade attenuated renal tissue phosphorylation of mTOR in HIVAN mice. In vitro studies, both renin and Ang II displayed enhanced mouse tubular cell (MTC) phosphorylation of p70S6K in a dose dependent manner. HIV/MTC also displayed enhanced phosphorylation of both mTOR and p70S6K; interestingly this effect of HIV was further enhanced by losartan (an AT1R blocker). On the other hand, AT2R blockade attenuated HIV-induced tubular cell phosphorylation of mTOR and p70S6K, whereas, AT2R agonist enhanced phosphorylation of mTOR and p70S6K. These findings indicate that HIV stimulates mTOR pathway in HIVAN through the activation of renin angiotensin system via AT2R.