Different effects of p58PITSLRE on the apoptosis induced by etoposide, cycloheximide and serum-withdrawal in human hepatocarcinoma cells

Thr-370 is responsible for CDK11(p58) autophosphorylation, dimerization, and kinase activity

CDK11(p58), a member of the p34(cdc2)-related kinase family, is associated with cell cycle progression, tumorigenesis, and proapoptotic signaling. It is also required for the maintenance of chromosome cohesion, the maturation of centrosome, the formation of bipolar spindle, and the completion of mitosis. Here we identified that CDK11(p58) interacted with itself to form homodimers in cells, whereas D224N, the kinase-dead mutant, failed to form homodimers. CDK11(p58) was autophosphorylated, and the main functions of CDK11(p58), such as kinase activity, transactivation of nuclear receptors, and proapoptotic signal transduction, were dependent on its autophosphorylation. Furthermore, the in vitro kinase assay indicated that CDK11(p58) was autophosphorylated at Thr-370. By mutagenesis, we created CDK11(p58) T370A and CDK11(p58) T370D, which mimic the dephosphorylated and phosphorylated forms of CDK11(p58), respectively. The T370A mutant could not form dimers and be phosphorylated by the wild type CDK11(p58) and finally lost the kinase activity. Further functional research revealed that T370A failed to repress the transactivation of androgen receptor and enhance the cell apoptosis. Overall, our data indicated that Thr-370 is responsible for the autophosphorylation, dimerization, and kinase activity of CDK11(p58). Moreover, Thr-370 mutants might affect CDK11(p58)-mediated signaling pathways.

Genetic variations of the CDC2L2 gene are associated with type 2 diabetes in a Han Chinese cohort

OBJECTIVE

The purpose of the present study was to study the potential association of CDC2L2 variations with type 2 diabetes (T2D).

METHODS

SNPs (single nucleotide polymorphisms) were extensively screened across the CDC2L2 gene by the site-specific PCR method ARMS (Amplification Refractory Mutation System). The identified novel polymorphisms were further evaluated in a Han Chinese cohort comprising of 467 patients with diabetes and 569 nondiabetic controls. In addition, 76 parent-offspring trios were also included in this association study. The case-control and TDT/sibTDT studies are applied for association analysis in this study.

RESULTS

Seven loci (rs1059831, SNP33, rs7528782, SNP11, SNP36, rs11488590 and SNP30) were shown to be significantly associated with T2D in unrelated individuals (p < 0.05). When individuals were stratified by age, sex and body mass index (BMI), the SNP11 was shown to be strongly associated with female patients with T2D, patients whose age was over 45 years and individuals whose BMI was less than 23 (p = 0.018, 0.011 and 0.0089, respectively). However, it was not replicated in the family-based TDT/sibTDT analysis (p = 0.085, OR = 0.63 (CI 95% 0.34-1.06)).

CONCLUSION

Our data suggested that the CDC2L2 gene may contribute to the susceptibility of type 2 diabetes in the northern Han Chinese population, but further studies are needed to replicate these findings.

CDK11(p58) protein kinase activity is associated with Bcl-2 down-regulation in pro-apoptosis pathway

CDK11(p58), a G2/M-specific protein kinase, has been shown to be associated with apoptosis in many cell lines, with largely unknown mechanisms. Our previous study proved that CDK11(p58)-enhanced cycloheximide (CHX)-induced apoptosis in SMMC-7721 hepatocarcinoma cells. Here we report for the first time that ectopic expression of CDK11(p58) down-regulates Bcl-2 expression and its Ser70, Ser87 phosphorylation in CHX-induced apoptosis in SMMC-7721 cells. Overexpression of Bcl-2 counteracts the pro-apoptotic activity of CDK11(p58). Furthermore, we confirm that the kinase activity of CDK11(p58) is essential to the down-regulation of Bcl-2 as well as apoptosis. Taken together, these results demonstrate that CDK11(p58) down-regulates Bcl-2 in pro-apoptosis pathway depending on its kinase activity, which elicits survival signal in hepatocarcinoma cells.

Induction of apoptosis by p110C requires mitochondrial translocation of the proapoptotic BCL-2 family member BAD

p110C, a 50-kDa isoform of the PITSLRE kinase family, was demonstrated to play an important role in cell apoptosis. However, how p110C exactly promotes apoptosis is unclear. Our previous study showed that p110C interacted with p21-activated kinase 1 (PAK1), an important kinase of the proapoptotic BCL-2 family member BAD, and evidently inhibited its kinase activity. Here, we report that overexpression of p110C leads to decreased phosphorylation of BAD and its subsequent translocation from cytosol to mitochondria, which in turn induces the release of cytochrome c and the onset of apoptosis. Knocking down endogenous BAD expression will inhibit p110C induced apoptosis. Two kinase dead forms of p110C, D149N and K36N, lose the ability to inhibit the kinase activity of PAK1 and fail to induce the translocation of BAD and the BAD and such proapoptotic ability is associated with the kinase activity of p110C.

Downregulation of beta1,4-galactosyltransferase 1 inhibits CDK11(p58)-mediated apoptosis induced by cycloheximide

Cyclin-dependent kinase 11 (CDK11; also named PITSLRE) is part of the large family of p34(cdc2)-related kinases whose functions appear to be linked with cell cycle progression, tumorigenesis, and apoptotic signaling. The mechanism that CDK11(p58) induces apoptosis is not clear. Some evidences suggested beta1,4-galactosyltransferase 1 (beta1,4-GT 1) might participate in apoptosis induced by CDK11(p58). In this study, we demonstrated that ectopically expressed beta1,4-GT 1 increased CDK11(p58)-mediated apoptosis induced by cycloheximide (CHX). In contrast, RNAi-mediated knockdown of beta1,4-GT 1 effectively inhibited apoptosis induced by CHX in CDK11(p58)-overexpressing cells. For example, the cell morphological and nuclear changes were reduced; the loss of cell viability was prevented and the number of cells in sub-G1 phase was decreased. Knock down of beta1,4-GT 1 also inhibited the release of cytochrome c from mitochondria and caspase-3 processing. Therefore, the cleavage of CDK11(p58) by caspase-3 was reduced. We proposed that beta1,4-GT 1 might contribute to the pro-apoptotic effect of CDK11(p58). This may represent a new mechanism of beta1,4-GT 1 in CHX-induced apoptosis of CDK11(p58)-overexpressing cells.

The C-terminal kinase domain of the p34cdc2-related PITSLRE protein kinase (p110C) associates with p21-activated kinase 1 and inhibits its activity during anoikis

The PITSLRE protein kinases are parts of the large family of p34cdc2-related kinases. During apoptosis induced by some stimuli, specific PITSLRE isoforms are cleaved by caspase to produce a protein that contains the C-terminal kinase domain of the PITSLRE proteins (p110C). The p110C induces apoptosis when it is ectopically expressed in Chinese hamster ovary cells. In our study, similar induction of this p110C was observed during anoikis in NIH3T3 cells. To investigate the molecular mechanism of apoptosis mediated by p110C, we used the yeast two-hybrid system to screen a human fetal liver cDNA library and identified p21-activated kinase 1 (PAK1) as an interacting partner of p110C. The association of p110C with PAK1 was further confirmed by in vitro binding assay, in vivo coimmunoprecipitation, and confocal microscope analysis. The interaction of p110C with PAK1 occurred within the residues 210-332 of PAK1. Neither association between p58PITSLRE or p110PITSLRE and PAK1 nor association between p110C and PAK2 or PAK3 was observed. Anoikis was increased and PAK1 activity was inhibited when NIH3T3 cells were transfected with p110C. Furthermore, the binding of p110C with PAK1 and inhibition of PAK1 activity were also observed during anoikis. Taken together, these data suggested that PAK1 might participate in the apoptotic pathway mediated by p110C.

Involvement of beta 1,4 galactosyltransferase 1 and Gal beta1-->4GlcNAc groups in human hepatocarcinoma cell apoptosis

Beta 1,4 galactosyltransferase 1 (beta 1,4GT1) synthesizes Gal beta 1-->4GlcNAc groups in N-linked sugar chains of animal glycoproteins, which have been demonstrated to play an important role in many biological events, including sperm-egg interaction, cell migration and mammalian embryonic development. In this study, the mRNA level of beta 1,4GT1 was found to increase greatly during the 7721 hepatocarcinoma cells apoptosis induced by cycloheximide. Ricinus Communis Agglutinin-I staining indicated generous increase of Gal beta 1-->4GlcNAc groups during apoptosis. Further study showed that the 7721 hepatocarcinoma cells transiently transfected with beta 1,4GT1 were more susceptible to the apoptosis induced by cycloheximide. The increased susceptibility was in accordance to the transfection concentration of beta 1,4GT1, which also led to the increased Gal beta 1-->4GlcNAc groups on the transfected cell surface. All the observations suggested that beta 1,4GT1 and Gal beta 1-->4GlcNAc groups might be associated with the apoptosis of human hepatocarcinoma cells.