HDAC3 Regulates Gingival Fibroblast Inflammatory Responses in Periodontitis

Histone deacetylases (HDACs) are important regulators of gene expression that are aberrantly regulated in several inflammatory and infectious diseases. HDAC inhibitors (HDACi) suppress inflammatory activation of various cell types through epigenetic and non-epigenetic mechanisms, and ameliorate pathology in a mouse model of periodontitis. Activation of gingival fibroblasts (GFs) significantly contributes to the development of periodontitis and the anaerobic bacterium Porphyromonas gingivalis plays a key role in driving chronic inflammation. Here, we analyzed the role of HDACs in inflammatory responses of GFs. Pan-HDACi suberoylanilide hydroxamic acid (SAHA) and/or ITF2357 (givinostat) significantly reduced TNFα- and P. gingivalis–inducible expression and/or production of a cluster of inflammatory mediators in healthy donor GFs (IL1B, CCL2, CCL5, CXCL10, COX2, and MMP3) without affecting cell viability. Selective inhibition of HDAC3/6, but not specific HDAC1, HDAC6, or HDAC8 inhibition, reproduced the suppressive effects of pan-HDACi on the inflammatory gene expression profile induced by TNFα and P. gingivalis, suggesting a critical role for HDAC3 in GF inflammatory activation. Consistently, silencing of HDAC3 expression with siRNA largely recapitulated the effects of HDAC3/6i on mRNA levels of inflammatory mediators in P. gingivalis–infected GFs. In contrast, P. gingivalis internalization and intracellular survival in GFs remained unaffected by HDACi. Activation of mitogen-activated protein kinases and NFκB signaling was unaffected by global or HDAC3/6-selective HDACi, and new protein synthesis was not required for gene suppression by HDACi. Finally, pan-HDACi and HDAC3/6i suppressed P. gingivalis–induced expression of IL1B, CCL2, CCL5, CXCL10, MMP1, and MMP3 in GFs from patients with periodontitis. Our results identify HDAC3 as an important regulator of inflammatory gene expression in GFs and suggest that therapeutic targeting of HDAC activity, in particular HDAC3, may be clinically beneficial in suppressing inflammation in periodontal disease.

MYC selects against reduced BCL2A1/A1 protein expression during B cell lymphomagenesis

Rearrangements of MYC or ABL proto-oncogenes lead to deregulated expression of key-regulators of cell cycle and cell survival, thereby constituting important drivers of blood cancer. Members of the BCL-2 family of apoptosis regulators contribute to oncogenic transformation downstream of these oncogenes, but the role of anti-apoptotic BCL2A1/A1 in transformation and drug resistance caused by deregulation of these oncogenes remains enigmatic. Here we analyzed the role of A1 in MYC as well as ABL kinase-driven blood cancer in mice, employing in vivo RNAi. We report that overexpression of either oncogene leads to a significant increase in A1 protein levels in otherwise A1-negative B cell progenitors, indicating a key role downstream of these oncogenes to secure survival during transformation. Knockdown of A1 by RNAi, however, did not impact on tumor latency in v-Abl-driven pre-B-ALL. In contrast, A1 knockdown in premalignant Eμ-MYC mice caused a significant reduction of transgenic pre-B cells without impacting on tumor latency as the emerging lymphomas escaped silencing of A1 expression. These findings identify A1 as a MYC target that can be induced prematurely during B cell development to aid expansion of otherwise cell-death-prone MYC transgenic pre-B cells. Hence, A1 should be considered as a putative drug target in MYC-driven blood cancer.

Conditional knockdown of BCL2A1 reveals rate-limiting roles in BCR-dependent B-cell survival

Bcl2 family proteins control mitochondrial apoptosis and its members exert critical cell type and differentiation stage-specific functions, acting as barriers against autoimmunity or transformation. Anti-apoptotic Bcl2a1/Bfl1/A1 is frequently deregulated in different types of blood cancers in humans but its physiological role is poorly understood as quadruplication of the Bcl2a1 gene locus in mice hampers conventional gene targeting strategies. Transgenic overexpression of A1, deletion of the A1-a paralogue or constitutive knockdown in the hematopoietic compartment of mice by RNAi suggested rate-limiting roles in lymphocyte development, granulopoiesis and mast cell activation. Here we report on the consequences of conditional knockdown of A1 protein expression using a reverse transactivator (rtTA)-driven approach that highlights a critical role for this Bcl2 family member in the maintenance of mature B-cell homeostasis. Furthermore, we define the A1/Bim (Bcl-2 interacting mediator of cell death) axis as a target of key kinases mediating B-cell receptor (BCR)-dependent survival signals, such as, spleen tyrosine kinase (Syk) and Brutons tyrosine kinase (Btk). As such, A1 represents a putative target for the treatment of B-cell-related pathologies depending on hyperactivation of BCR-emanating survival signals and loss of A1 expression accounts, in part, for the pro-apoptotic effects of Syk- or Btk inhibitors that rely on the ‘BH3-only' protein Bim for cell killing.