Developmental Regulators Containing the I-mfa Domain Interact with T cyclins and Tat and Modulate Transcription

Abstract

SummaryPositive transcription elongation factor b (P-TEFb) complexes, composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1 or T2, are engaged by many cellular transcription regulators that activate or inhibit transcription from specific promoters. The related I-mfa (inhibitor of MyoD family a) and HIC (human I-mfa-domain-containing) proteins function in myogenic differentiation and embryonic development by participating in the Wnt signaling pathway. We report that I-mfa is a novel regulator of P-TEFb. Both HIC and I-mfa interact through their homologous I-mfa domains with cyclin T1 and T2 at two binding sites. One site is the regulatory histidine-rich domain that interacts with CDK9 substrates including RNA polymerase II. The second site contains a lysine-and arginine-rich motif that is highly conserved between the two T cyclins. This site overlaps and includes the previously identified Tat/TAR recognition motif of cyclin T1 required for activation of human immunodeficiency virus type 1 (HIV-1) transcription. HIC and I-mfa can serve as substrates for PTEFb. Their I-mfa domains also bind the activation domain of HIV-1 Tat and inhibit Tat-and PTEFb-dependent transcription from the HIV-1 promoter. This transcriptional repression is cell-type specific and can operate via Tat and cyclin T1. Genomic and sequence comparisons indicate that the I-mf and HIC genes, as well as flanking genes, diverged from a duplicated chromosomal region. Our findings link I-mfa and HIC to viral replication and suggest that P-TEFb is modulated in the Wnt signaling pathway.

Expression profile and differential regulation of the Human I-mfa domain-Containing protein (HIC) gene in immune cells

“…The cell lines MT-2 (T cell leukemia), CEM (T cell leukemia), THP-1 (acute monocytic leukemia) and U937 (monocytic leukemia) all showed greater expression of HIC mRNA, relative to 293T (up to 4 times greater). On the other hand, the B lymphoblastoid cell lines Raji and BJAB showed lower or no HIC expression, relative to 293T cells, and no signal was detected in Jurkats, a T cell leukemia-derived cell line, in agreement with a previous study by Wang et al (2007) [13].…”

“…HIC has also been shown to interact with the Epstein-Barr viral protein RK-BARF0, although the functional relevance of this interaction has not been investigated [11]. In parallel, HIC has also been shown to interact with several cellular transcription factors, including Axin, cyclin T1 and TCF1, and to modulate their function and/or associated signaling pathways [10,12,13].…”

“…Northen Blot analyses have shown that in addition to prostate, uterus, and small intestine, HIC mRNA is expressed in human lymphoid organs including thymus, spleen and peripheral blood leukocytes but is almost absent in testis and colon [1]. End-point RT-PCR have shown that HIC is differentially expressed in various cell lines including cell lines of immune origin [13].…”

The Complex Regulation of HIC (Human I-mfa Domain Containing Protein) Expression

“…HIC has also been reported to affect the Wnt pathway [3], the JNK/SAPK pathway [3] and the activity of positive transcription elongation factor-b (P-TEFb) [4], [7], [8]. Cigognini et al recently studied chromosome 7 deletions in myeloid disorders [9].…”

Function of CDK12 in Tumor Initiation and Progression and Its Clinical Consequences

“…Primárně se tak děje v důsledku bodových nebo frameshift mutací či nukleotidových záměn, které jsou nejčastěji lokalizovány v kiná-zové doméně (2/ 3 mutací) a ve většině případů vedou ke ztrátě kinázové aktivity žení exprese pouze malé skupiny genů bez výrazného efektu na transkripci jako celek [11,19,32,34,35]. Z pohledu kancerogeneze je velmi důležitým zjištění, že onou specifi ckou skupinou CDK12 regulovaných genů jsou právě geny účastnící se, kromě jiného, odpovědi buňky na poškození DNA (damage response/ repair pathway -DDR): BRCA1, ATM, ATR, FANCI a FANCD2.…”