Effects of changes in calmodulin levels on cell proliferation

A TRPV1-to-secretagogin regulatory axis controls pancreatic β-cell survival by modulating protein turnover

Ca2+-sensor proteins are generally implicated in insulin release through SNARE interactions. Here, secretagogin, whose expression in human pancreatic islets correlates with their insulin content and the incidence of type 2 diabetes, is shown to orchestrate an unexpectedly distinct mechanism. Single-cell RNA-seq reveals retained expression of the TRP family members in β-cells from diabetic donors. Amongst these, pharmacological probing identifies Ca2+-permeable transient receptor potential vanilloid type 1 channels (TRPV1) as potent inducers of secretagogin expression through recruitment of Sp1 transcription factors. Accordingly, agonist stimulation of TRPV1s fails to rescue insulin release from pancreatic islets of glucose intolerant secretagogin knock-out(-/-) mice. However, instead of merely impinging on the SNARE machinery, reduced insulin availability in secretagogin-/- mice is due to β-cell loss, which is underpinned by the collapse of protein folding and deregulation of secretagogin-dependent USP9X deubiquitinase activity. Therefore, and considering the desensitization of TRPV1s in diabetic pancreata, a TRPV1-to-secretagogin regulatory axis seems critical to maintain the structural integrity and signal competence of β-cells.

The many faces of calmodulin in cell proliferation, programmed cell death, autophagy, and cancer

Calmodulin (CaM) is a ubiquitous Ca(2+) receptor protein mediating a large number of signaling processes in all eukaryotic cells. CaM plays a central role in regulating a myriad of cellular functions via interaction with multiple target proteins. This review focuses on the action of CaM and CaM-dependent signaling systems in the control of vertebrate cell proliferation, programmed cell death and autophagy. The significance of CaM and interconnected CaM-regulated systems for the physiology of cancer cells including tumor stem cells, and processes required for tumor progression such as growth, tumor-associated angiogenesis and metastasis are highlighted. Furthermore, the potential targeting of CaM-dependent signaling processes for therapeutic use is discussed.

Hepatic in vitro toxicity assessment of PBDE congeners BDE47, BDE153 and BDE154 in Atlantic salmon (Salmo salar L.)

The brominated flame retardant congeners BDE47, BDE153 and BDE154 are among the congeners accumulating to the highest degree in fish. In order to gain knowledge about the toxicological effects of PBDEs in fish, microarray-based transcriptomic and 2D-DIGE/MALDI-TOF/TOF proteomic approaches were used to screen for effects in primary Atlantic salmon hepatocytes exposed to these congeners alone or in combination (PBDE-MIX). A small set of stress related transcripts and proteins were differentially expressed in the PBDE exposed hepatocytes. The PBDE-MIX, and BDE153 to a lesser degree, seems to have induced metabolic disturbances by affecting several pathways related to glucose homeostasis. Further, effects on cell cycle control and proliferation signal pathways in PBDE-MIX-exposed hepatocytes clearly suggest that the PBDE exposure affected cell proliferation processes. CYP1A was 7.41- and 7.37-fold up-regulated in hepatocytes exposed to BDE47 and PBDE-MIX, respectively, and was the only biotransformation pathway affected by the PBDE exposure. The factorial design and PLS regression analyses of the effect of the PBDE-MIX indicated that BDE47 contributed the most to the observed CYP1A response, suggesting that this congener should be incorporated in the toxic equivalent (TEQ) concept in future risk assessment of dioxin-like chemicals. Additionally, a significant up-regulation of the ER-responsive genes VTG and ZP3 was observed in cells exposed to BDE47 and PBDE-MIX. Further analyses suggested that BDE47 and BDE154 have an estrogenic effect in male fish. The data also suggested an antagonistic interaction between BDE153 and BDE154. In conclusion, this study shows that PBDEs can affect several biological systems in Atlantic salmon cells, and demonstrates the need for more studies on the simultaneous exposure to chemical mixtures to identify combined effects of chemicals.

Proteomic analysis of testis biopsies in men treated with injectable testosterone undecanoate alone or in combination with oral levonorgestrel as potential male contraceptive

Treatment with injectable testosterone undecanoate (TU) alone or in combination with oral levonorgestrel (LNG) resulted in marked decreases in sperm concentrations. In this study, we used proteomic analyses to examine the cellular/molecular events occurring in the human testis after TU or TU + LNG treatment. We conducted a global proteomic analysis of the human testicular biopsies before and at 2 weeks after TU alone or TU + LNG treatment. Proteins showing significant changes in expression were identified and analyzed. As a result, 17 and 46 protein spots were found with significant differential expression after the treatment with TU alone and TU + LNG, respectively. TU treatment changed the expression of heterogeneous nuclear ribonucleoprotein K (hnRNP K), proteasome inhibitor PI31 subunit (PSMF1), and superoxide dismutase [Mn] mitochondrial precursor (SOD2). These proteins inhibit "assembly", induce cell death, and promote compensatory "cell survival" in the testis. After TU + LNG treatment, "proliferation/cell survival" and "apoptosis/death" were the predominant responses in the testis. TU + LNG treatment inhibited the expression of Prolyl 4-hydroxylase beta subunit (P4HB) and Annexin A2 (Annexin II). These proteins are involved in apoptosis and cell proliferation, respectively. TU + LNG treatment also enhanced the expression of SOD2 and Parvalbumin alpha (Pvalb). These two proteins may protect testicular cells against apoptosis/death and promote cell survival. In conclusion, TU and TU + LNG treatments suppress spermatogenesis through different pathways by changing the expression of different proteins. hnRNP K, PSMF1, SOD2, P4HB, Annexin II, and Pvalb, are key proteins that may be early molecular targets responsible for spermatogenesis suppression induced by hormone treatment.

Effects of tyroserleutide on gene expression of calmodulin and PI3K in hepatocellular carcinoma

Tyroserleutide (YSL) is a tripeptide compound that has exhibited inhibitory effects on hepatocellular carcinoma in our previous research. The mechanism of this antitumor activity involves the second messenger, Ca(2+). Ca(2+) influences cell function through the Ca(2+)/calmodulin (CaM) pathway, and abnormality of the Ca(2+)/CaM system correlates closely with the occurrence of tumors. In addition, CaM associates with phosphatidylinositol 3 kinase (PI3K), thereby enhancing the activity of PI3K, which promotes cell proliferation. In order to investigate its anti-tumor mechanism, we studied the effects of YSL on CaM protein expression and mRNA level, PI3K activity, PI3K regulatory subunit p85 protein expression and mRNA level, and the mRNA level of PI3K catalytic subunits p110alpha and p110gamma in human hepatocellular carcinoma BEL-7402 xenograft tumors in nude mice. Our results showed that YSL decreased the mRNA level and protein expression of CaM, inhibited the activity of PI3K, and reduced the mRNA level and protein expression of the PI3K regulatory subunit p85 and mRNA level of PI3K catalytic subunits p110alpha and p110gamma. Accordingly, it is suggestive that the anti-tumor effects of YSL may be mediated by down regulation of CaM and PI3K subunits p85 and p110, influencing the signal transduction pathway in the tumor cells and perhaps overcoming the dysfunctional PI3K activity in tumors.

Calmodulin mediates sulfur mustard toxicity in human keratinocytes

Sulfur mustard (SM) causes blisters in the skin through a series of cellular changes that we are beginning to identify. We earlier demonstrated that SM toxicity is the result of induction of both death receptor and mitochondrial pathways of apoptosis in human keratinocytes (KC). Because of its importance in apoptosis in the skin, we tested whether calmodulin (CaM) mediates the mitochondrial apoptotic pathway induced by SM. Of the three human CaM genes, the predominant form expressed in KC was CaM1. RT-PCR and immunoblot analysis revealed upregulation of CaM expression following SM treatment. To delineate the potential role of CaM1 in the regulation of SM-induced apoptosis, retroviral vectors expressing CaM1 RNA in the antisense (AS) orientation were used to transduce and derive stable CaM1 AS cells, which were then exposed to SM and subjected to immunoblot analysis for expression of apoptotic markers. Proteolytic activation of executioner caspases-3, -6, -7, and the upstream caspase-9, as well as caspase-mediated PARP cleavage were markedly inhibited by CaM1 AS expression. CaM1 AS depletion attenuated SM-induced, but not Fas-induced, proteolytic processing and activation of caspase-3. Whereas control KC exhibited a marked increase in apoptotic nuclear fragmentation after SM, CaM1 AS cells exhibited normal nuclear morphology up to 48h after SM, indicating that suppression of apoptosis in CaM1 AS cells increases survival and does not shift to a necrotic death. CaM has been shown to activate the phosphatase calcineurin, which can induce apoptosis by Bad dephosphorylation. Interestingly, whereas SM-treated CaM1-depleted KC expressed the phosphorylated non-apoptotic sequestered form of Bad, Bad was present in the hypophosphorylated apoptotic form in SM-exposed control KC. To determine if pharmacological CaM inhibitors could attenuate SM-induced apoptosis via Bad dephosphorylation, KC were pretreated with the CaM-specific antagonist W-13 or its less active structural analogue W-12. Following SM exposure, KC exhibited Bad dephosphorylation, which was inhibited in the presence of W-13, but not with W-12. Consequently, W-13 but not W-12 markedly suppressed SM-induced proteolytic processing and activation of caspase-3, as well as apoptotic nuclear fragmentation. Finally, while the CaM antagonist W-13 and the calcineurin inhibitor cyclosporin A attenuated SM-induced caspase-3 activation, inhibitors for CaM-dependent protein kinase II (KN62 and KN93) did not. These results indicate that CaM, calcineurin, and Bad also play a role in SM-induced apoptosis, and may therefore be targets for therapeutic intervention to reduce SM injury.

Effect of antisense oligodeoxynucleotides directed to individual calmodulin gene transcripts on the proliferation and differentiation of PC12 cells

Calmodulin (CaM) is encoded by three different genes that collectively give rise to five transcripts. In the present study, we used antisense oligodeoxynucleotides targeted to unique sequences in the transcripts from the individual CaM genes to selectively block the expression of the different genes and to investigate the roles these individual genes play in the proliferation and nerve growth factor (NGF)-induced differentiation of PC12 cells. Culturing PC12 cells in the presence of oligodeoxynucleotide antisense to the transcripts from CaM genes I and II caused a significant decrease in the proliferation and a significant delay in the NGF-induced differentiation of PC12 cells when compared with untreated cells and with cells treated with the corresponding randomized oligodeoxynucleotides. However, an oligodeoxynucleotide antisense to CaM gene III did not significantly alter the proliferation or the NGF-induced differentiation of PC12 cells. The inhibition of cell proliferation could be reversed by washing out the antisense oligodeoxynucleotides. The levels of CaM in cells treated with oligodeoxynucleotides antisense to CaM genes I or II were reduced 52% or 63%, respectively, of the levels found in the control cells. However, the levels of CaM were not significantly reduced in PC12 cells treated with CaM gene III antisense oligodeoxynucleotide. None of the randomized oligodeoxynucleotides had any effect on the levels of CaM in PC12 cells. The reduced levels of CaM in PC12 cells treated with an oligodeoxynucleotide antisense to CaM gene I were accompanied by a reduction in the levels of the CaM gene I mRNAs, supporting a true antisense mechanism of action for these oligodeoxynucleotides. These results suggest that altering the level of CaM by using antisense oligodeoxynucleotides targeted to the dominant CaM transcripts in a particular cell type will specifically inhibit their proliferation and, in the case of neuronal cells, alter the course of their differentiation.

Functional consequences in yeast of single-residue alterations in a consensus calmodulin

A synthetic gene encoding a ‘consensus’ calmodulin (synCaM) was able to substitute for the Saccharomyces cerevisiae calmodulin gene (CMDI), even though synCaM is only 60% identical in primary amino acid sequence to yeast Cmd1. Twelve different synCaM mutants were also expressed in yeast. Seven of the 12 mutant synCaMs supported germination and growth of Cmd1-deficient spores. Five of the 12 mutant synCaMs were incapable of supporting germination of Cmd1-deficient spores and, of these, four were also incapable of supporting vegetative growth of Cmd1-deficient haploid cells. The five nonfunctional synCaM mutants were expressed at levels equivalent to, or higher than, the seven synCaM mutants that were able to substitute for Cmd1; thus, the inability to function was not simply due to inadequate expression or rapid degradation. All nonfunctional synCaM mutants shared a single charge reversal mutation in the central helix (E84K), which was found to be sufficient to confer the lethal phenotype. The ability of another mutant synCaM (S101F) to support growth of Cmd1-deficient cells was dependent on cell ploidy. Another mutant (K115Y) supported spore germination and vegetative growth, but not meiosis and sporulation. The terminal phenotype of cells lacking a functional calmodulin included a dramatic accumulation of polymerized microtubules.