An Alternatively Translated Connexin 43 Isoform, GJA1-11k, Localizes to the Nucleus and Can Inhibit Cell Cycle Progression

Connexin 43 (Cx43) is a gap junction protein that assembles at the cell border to form intercellular gap junction (GJ) channels which allow for cell–cell communication by facilitating the rapid transmission of ions and other small molecules between adjacent cells. Non-canonical roles of Cx43, and specifically its C-terminal domain, have been identified in the regulation of Cx43 trafficking, mitochondrial preconditioning, cell proliferation, and tumor formation, yet the mechanisms are still being explored. It was recently identified that up to six truncated isoforms of Cx43 are endogenously produced via alternative translation from internal start codons in addition to full length Cx43, all from the same mRNA produced by the gene GJA1. GJA1-11k, the 11kDa alternatively translated isoform of Cx43, does not have a known role in the formation of gap junction channels, and little is known about its function. Here, we report that over expressed GJA1-11k, unlike the other five truncated isoforms, preferentially localizes to the nucleus in HEK293FT cells and suppresses cell growth by limiting cell cycle progression from the G0/G1 phase to the S phase. Furthermore, these functions are independent of the channel-forming full-length Cx43 isoform. Understanding the apparently unique role of GJA1-11k and its generation in cell cycle regulation may uncover a new target for affecting cell growth in multiple disease models.

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Abstract 235: GJA1-11k Localizes to the Nucleus and Inhibits Cell Cycle Progression

Circulation Research ◽

10.1161/res.121.suppl_1.235 ◽

2017 ◽

Vol 121 (suppl_1) ◽

Author(s):

Irina Epifantseva ◽

Shaohua Xiao ◽

Nan Deng ◽

TingTing Hong ◽

Robin Shaw

Keyword(s):

Cell Cycle ◽

Cell Growth ◽

Connexin 43 ◽

Cell Cycle Progression ◽

Full Length ◽

Cycle Progression ◽

Alternative Translation ◽

Rapid Transmission ◽

Potent Growth ◽

Internal Translation

Gap Junction (GJ) channels, including the most common Connexin 43 (Cx43), are involved in the exchange of ions and small molecules to maintain homeostasis and also have fundamental roles in excitable tissues by facilitating rapid transmission of action potentials between adjacent cells. For instance, synchronization during each heartbeat is regulated by these ion channels at the cardiomyocyte cell-cell border. Numerous studies have found that Cx43 (predominantly the C-domain) is associated with control of cell proliferation, yet it is unclear how Cx43-based membrane channels effect these processes. We recently identified the existence of six endogenous Cx43 isoforms which are produced from the same full-length mRNA molecule in human cells by means of alternative translation and many of the known non-canonical roles of Cx43 can be attributed to these recently identified isoforms. Here we report that the smaller, non-channel related, alternatively translated isoform of Cx43 can directly affect cell growth. We found that 11KDa isoform (GJA1-11k) is localized in the nucleus of HEK293FT cells. GJA1-11k is a more potent growth suppressor than the wild type and full length isoform GJA1-43k. GJA1-11k-mediated growth suppression was achieved by limiting cell cycle progression from G0/G1 to S phase, in part, through regulation of internal translation of GJA1-11k. Nuclear localization experiments indicate that the cell growth-suppressive properties of GJA1-11k is linked to nuclear activity. RNA-seq based genome-wide mRNA transcriptome analysis revealed that the heat shock protein HSPA6, which is normally upregulated in certain cancer cells, was significantly downregulated in GJA1-11k overexpressing cells compared to cells overexpressing the full length isoform, suggesting a potential mechanism and/or new binding protein for the Cx43 C-terminal domain. In general, further understanding of the role of small Cx43 isoforms will provide a way not only to understand the mechanism controlling myocyte proliferation to improve the repair of the myocardium, but also to understand the pathobiology of cell growth associated with tumor suppressive properties of Cx43. It may be possible to develop new therapeutics by regulating alternative translation of Cx43.

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Oncogenic role of ALX3 in cervical cancer cells through KDM2B-mediated histone demethylation of CDC25A

BMC Cancer ◽

10.1186/s12885-021-08552-7 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Jinhong Qi ◽

Li Zhou ◽

Dongqing Li ◽

Jingyuan Yang ◽

He Wang ◽

...

Keyword(s):

Cell Cycle ◽

Cervical Cancer ◽

Cell Growth ◽

Cancer Cells ◽

Cell Cycle Progression ◽

Cervical Squamous Cell Carcinoma ◽

Cycle Progression ◽

Normal Tissues ◽

Positive Regulator ◽

Cervical Cancer Cells

Abstract Background Cell division cycle 25A (CDC25A) is a well-recognized regulator of cell cycle progression and is involved in cancer development. This work focused on the function of CDC25A in cervical cancer cell growth and the molecules involved. Methods A GEO dataset GSE63514 comprising data of cervical squamous cell carcinoma (CSCC) tissues was used to screen the aberrantly expressed genes in cervical cancer. The CDC25A expression in cancer and normal tissues was predicted in the GEPIA database and that in CSCC and normal cells was determined by RT-qPCR and western blot assays. Downregulation of CDC25A was introduced in CSCC cells to explore its function in cell growth and the cell cycle progression. The potential regulators of CDC25A activity and the possible involved signaling were explored. Results CDC25A was predicted to be overexpressed in CSCC, and high expression of CDC25A was observed in CSCC cells. Downregulation of CDC25A in ME180 and C33A cells reduced cell proliferation and blocked cell cycle progression, and it increased cell apoptosis. ALX3 was a positive regulator of CDC25A through transcription promotion. It recruited a histone demethylase, lysine demethylase 2B (KDM2B), to the CDC25A promoter, which enhanced CDC25A expression through demethylation of H3k4me3. Overexpression of ALX3 in cells blocked the inhibitory effects of CDC25A silencing. CDC25A was found as a positive regulator of the PI3K/Akt signaling pathway. Conclusion This study suggested that the ALX3 increased CDC25A expression through KDM2B-mediated demethylation of H3K4me3, which induced proliferation and cell cycle progression of cervical cancer cells.

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Cell cycle progression: computer simulation of uncoupled subcycles of DNA replication and cell growth

Journal of Theoretical Biology ◽

10.1006/jtbi.1995.0130 ◽

1995 ◽

Vol 175 (2) ◽

pp. 177-189 ◽

Cited By ~ 9

Author(s):

Roland Sennerstam ◽

Jan-Olof Strömberg

Keyword(s):

Cell Cycle ◽

Computer Simulation ◽

Dna Replication ◽

Cell Growth ◽

Cell Cycle Progression ◽

Cycle Progression

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Distinct and sequential upregulation of genes regulating cell growth and cell cycle progression during hepatic ischemia-reperfusion injury

AJP Cell Physiology ◽

10.1152/ajpcell.00629.2004 ◽

2005 ◽

Vol 289 (4) ◽

pp. C826-C835 ◽

Cited By ~ 41

Author(s):

Sharon Barone ◽

Tomohisa Okaya ◽

Steve Rudich ◽

Snezana Petrovic ◽

Kathy Tenrani ◽

...

Keyword(s):

Cell Cycle ◽

Cell Proliferation ◽

Cell Growth ◽

Reperfusion Injury ◽

Cell Cycle Progression ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Catabolic Pathway ◽

Cycle Progression

Ischemia-reperfusion injury (IRI) in liver and other organs is manifested as an injury phase followed by recovery and resolution. Control of cell growth and proliferation is essential for recovery from the injury. We examined the expression of three related regulators of cell cycle progression in liver IRI: spermidine/spermine N-acetyltransferase (SSAT), p21 (a cyclin-dependent kinase inhibitor), and stathmin. Mice were subjected to hepatic IRI, and liver tissues were harvested at timed intervals. The expression of SSAT, the rate-limiting enzyme in the polyamine catabolic pathway, had increased fivefold 6 h after IRI and correlated with increased putrescine levels in the liver, consistent with increased SSAT enzymatic activity in IRI. The expression of p21, which is transactivated by p53, was undetectable in sham-operated animals but was heavily induced at 12 and 24 h of reperfusion and declined to undetectable baseline levels at 72 h of reperfusion. The interaction of the polyamine pathway with the p53-p21 pathway was shown in vitro, where activation of SSAT with polyamine analog or the addition of putrescine to cultured hepatocytes induced the expression of p53 and p21 and decreased cell viability. The expression of stathmin, which is under negative transcriptional regulation by p21 and controls cell proliferation and progression through mitosis, remained undetectable at 6, 12, and 24 h of reperfusion and was progressively and heavily induced at 48 and 72 h of reperfusion. Double-immunofluorescence labeling with antibodies against stathmin and PCNA, a marker of cell proliferation, demonstrated colocalization of stathmin and PCNA at 48 and 72 h of reperfusion in hepatocytes, indicating the initiation of cell proliferation. The distinct and sequential upregulation of SSAT, p21, and stathmin, along with biochemical activation of the polyamine catabolic pathway in IRI in vivo and the demonstration of p53-p21 upregulation by SSAT and putrescine in vitro, points to the important role of regulators of cell growth and cell cycle progression in the pathophysiology and/or recovery in liver IRI. The data further suggest that SSAT may play a role in the initiation of injury, whereas p21 and stathmin may be involved in the resolution and recovery after liver IRI.

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Inactivation of CtIP Leads to Early Embryonic Lethality Mediated by G1 Restraint and to Tumorigenesis by Haploid Insufficiency

Molecular and Cellular Biology ◽

10.1128/mcb.25.9.3535-3542.2005 ◽

2005 ◽

Vol 25 (9) ◽

pp. 3535-3542 ◽

Cited By ~ 94

Author(s):

Phang-Lang Chen ◽

Feng Liu ◽

Suna Cai ◽

Xiaoqin Lin ◽

Aihua Li ◽

...

Keyword(s):

Cell Cycle ◽

Transcriptional Repression ◽

Cell Cycle Progression ◽

Tumor Formation ◽

3T3 Cells ◽

Embryonic Fibroblasts ◽

Cycle Progression ◽

Early Embryonic Lethality ◽

Nih 3T3 ◽

Regulate Cell Cycle Progression

ABSTRACT CtIP interacts with a group of tumor suppressor proteins including RB (retinoblastoma protein), BRCA1, Ikaros, and CtBP, which regulate cell cycle progression through transcriptional repression as well as chromatin remodeling. However, how CtIP exerts its biological function in cell cycle progression remains elusive. To address this issue, we generated an inactivated Ctip allele in mice by inserting a neo gene into exon 5. The corresponding Ctip − / − embryos died at embryonic day 4.0 (E4.0), and the blastocysts failed to enter S phase but accumulated in G1, leading to a slightly elevated cell death. Mouse NIH 3T3 cells depleted of Ctip were arrested at G1 with the concomitant increase in hypophosphorylated Rb and Cdk inhibitors, p21. However, depletion of Ctip failed to arrest Rb − / − mouse embryonic fibroblasts (MEF) or human osteosarcoma Saos-2 cells at G1, suggesting that this arrest is RB dependent. Importantly, the life span of Ctip +/ − heterozygotes was shortened by the development of multiple types of tumors, predominantly, large lymphomas. The wild-type Ctip allele and protein remained detectable in these tumors, suggesting that haploid insufficiency of Ctip leads to tumorigenesis. Taken together, this finding uncovers a novel G1/S regulation in that CtIP counteracts Rb-mediated G1 restraint. Deregulation of this function leads to a defect in early embryogenesis and contributes, in part, to tumor formation.

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