Identification and characterization of a novel testis-specific gene CKT2, which encodes a substrate for protein kinase CK2

Protein kinase CK2 is a serine/threonine kinase known to phosphorylate numerous substrates. CK2 is implicated in several physiologic and pathologic processes, particularly in cancer biology. CK2 is comprised of several subunits, including CK2α, CK2α′ and CK2β. Inactivation of CK2α′ leads to chromatin degeneration of germ cells, resulting in male sterility. To identify additional targets of CK2α′ in testes and to determine the role of CK2α′ in germ cell nuclear integrity, GST pull-down and protein–protein interaction assays were conducted. A novel testis-specific gene, CKT2 (CK2 Target protein 2), was found whose product interacts with and is phosphorylated by CK2 in vitro and in vivo. CKT2 is a 30.2 kDa protein with one coiled-coil domain and six putative phosphorylation sites. High expression of CKT2 correlated with chromatin condensation of spermatids in murine testes. Findings reported herein demonstrate that CKT2 is a target protein of native CK2α′ in testes and suggest that CKT2 plays a role in chromatin regulation of male germ cells

Protein kinase CK2-mediated phosphorylation of HDAC2 regulates co-repressor formation, deacetylase activity and acetylation of HDAC2 by cigarette smoke and aldehydes

Histone deacetylase 2 (HDAC2) mediates the repression of pro-inflammatory genes by deacetylating core histones, RelA/p65 and the glucocorticoid receptor. Reduced level of HDAC2 is associated with steroid resistant inflammation caused by oxidants. However, the molecular mechanisms regulating HDAC2 in response to oxidants and unsaturated aldehydes is not known. Here, we report that oxidative stress imposed by cigarette smoke extract (CSE), and aldehyde acrolein induced phosphorylation of HDAC2 which was abolished by serine-alanine mutations at serine sites S(394), S(411), S(422) and S(424). HDAC2 phosphorylation required direct interaction with serine-phosphorylated protein kinase CK2α and involved reduced HDAC2 deacetylase activity. Furthermore, HDAC2 phosphorylation was required for HDAC2 interaction with transcription factors, co-repressor complex formation, CBP recruitment, acetylation on lysine residues and consequently increased transrepression activity. Thus, phospho-acetylation of HDAC2 negatively regulates its deacetylase activity which has implications in steroid resistance in chronic inflammatory conditions

Functional Significance for a Heterogenous Ribonucleoprotein A18 Signature RNA Motif in the 3′-Untranslated Region of Ataxia Telangiectasia Mutated and Rad3-related (ATR) Transcript*

The predominantly nuclear heterogenous ribonucleoprotein A18 (hnRNP A18) translocates to the cytosol in response to cellular stress and increases translation by specifically binding to the 3′-untranslated region (UTR) of several mRNA transcripts and the eukaryotic initiation factor 4G. Here, we identified a 51-nucleotide motif that is present 11.49 times more often in the 3′-UTR of hnRNP A18 mRNA targets than in the UniGene data base. This motif was identified by computational analysis of primary sequences and secondary structures of hnRNP A18 mRNA targets against the unaligned sequences. Band shift analyses indicate that the motif is sufficient to confer binding to hnRNP A18. A search of the entire UniGene data base indicates that the hnRNP A18 motif is also present in the 3′-UTR of the ataxia telangiectasia mutated and Rad3-related (ATR) mRNA. Validation of the predicted hnRNP A18 motif is provided by amplification of endogenous ATR transcript on polysomal fractions immunoprecipitated with hnRNP A18. Moreover, overexpression of hnRNP A18 results in increased ATR protein levels and increased phosphorylation of Chk1, a preferred ATR substrate, in response to UV radiation. In addition, our data indicate that inhibition of casein kinase II or GSK3β significantly reduced hnRNP A18 cytosolic translocation in response to UV radiation. To our knowledge, this constitutes the first demonstration of a post-transcriptional regulatory mechanism for ATR activity. hnRNP A18 could thus become a new target to trigger ATR activity as back-up stress response mechanisms to functionally compensate for absent or defective responders

Hypoxia-inducible Factor 1α Induces Corticosteroid-insensitive Inflammation via Reduction of Histone Deacetylase-2 Transcription*

Corticosteroids are potent anti-inflammatory agents, but corticosteroid insensitivity is a major barrier for the treatment of some chronic inflammatory diseases. Here, we show that hypoxia induces corticosteroid-insensitive inflammation via reduced transcription of histone deacetylase-2 (HDAC2) in lung epithelial and macrophage cells. HDAC2 mRNA and protein expression was reduced under hypoxic conditions (1% O2). Hypoxia enhanced interleukin-1β-induced interleukin-8 (CXCL8) production in A549 cells and decreased the ability of dexamethasone to suppress the CXCL8 production. Deletion or point mutation studies revealed that binding of the transcription factor hypoxia-inducible factor (HIF) 1α to a HIF response element at position −320, but not HIF-1β or HIF-2α, results in reduced polymerase II binding at the site, leading to reduced promoter activity of HDAC2. Our results suggest that activation of HIF-1α by hypoxia decreases HDAC2 levels, resulting in amplified inflammation and corticosteroid resistance