BIS overexpression does not affect the sensitivity of HEK 293T cells against apoptosis

SRSF3 Is a Critical Requirement for Inclusion of Exon 3 of BIS Pre-mRNA

BCL-2 interacting cell death suppressor (BIS), also known as BAG3, is a multifunctional protein. Aberrant expression and mutation of BIS have been implicated in cancers and myopathy. However, there have only been a few studies on the splicing of BIS pre-mRNA. In the present study, through RT-PCR and sequencing in various cell lines and mouse tissues, we identified for the first time the presence of BIS mRNA isomers in which exon 3 or exons 2–3 are skipped. We also demonstrated that the depletion of SRSF3 promoted the skipping of exon 3 of BIS pre-mRNA in endogenous BIS and the GFP-BIS minigene. SRSF3 specifically interacts with the putative binding sites in exon 3, in which deletion promoted the skipping of exon 3 in the GFP-BIS minigene, which was comparable to the effect of SRSF knockdown. Even though acceleration of exon 3 skipping was not observed in response to various stimuli, SRSF3 depletion, accompanied by the production of a truncated BIS protein, inhibited the nuclear translocation of HSF1, which was restored by the wild-type BIS, not by exon 3-depleted BIS. Therefore, our results suggested that the maintenance of SRSF3 levels and subsequent preservation of the intact BIS protein is an important factor in modulating HSF1 localization upon cellular stress.

Apoptosis and G2/M cell cycle arrest induced by a timosaponin A3 from Anemarrhena asphodeloides Bunge on AsPC-1 pancreatic cancer cells

BACKGROUND

Timosaponin A3 (TA3), one of the active components of spirostanol saponin isolated from A. asphodeloides, is widely used as an anticancer agent in a variety of cancer cell lines. However, the research on the anticancer efficacy is very limited in human pancreatic cancer models.

PURPOSE

In this study, we investigated the molecular targets in the active components of A. asphodeloides, which showed anti-cancer effects in human pancreatic cancer cells, and confirmed the pathways involved.

STUDY DESIGN

The apoptotic effects of five solvent extracts of A. asphodeloides in human pancreatic cancer cells (AsPC-1) was studied, and the phytochemical leading to their effects identified. Next, we determined whether the phytochemical inhibit STAT3 and ERK1/2, and investigated the pathways involved.

METHODS

Five solvent extracts of A. asphodeloides (100  µg/ml, 24  h) was investigated for their cytotoxicity against AsPC-1 cells. The active ingredient of the extract exhibiting the highest toxicity were analyzed by liquid chromatography-mass spectrometry. Next, we studied the mechanism of action of the phytochemical in pancreatic cancer. Cell cycle and annexin V/FITC assays were performed to assess cell growth and apoptosis capacity. The effects on apoptosis and proliferation-related pathways, STAT3, and MAPKs were confirmed at the protein level using immunoblotting. The factors regulated in the pathways were investigated using reverse transcription polymerase chain reaction.

RESULTS

The results showed that the ethyl acetate extract of A. asphodeloides (EAA) induced apoptotic and anti-proliferative activities through the STAT3 and MAPKs pathways. We found that TA3, an active component of EAA, inhibits constitutive STAT3 and ERK1/2 proteins. EAA and TA3 decreased the viability of AsPC-1 cells, leading to cell cycle arrest at the sub-G1 and G2/M phases. Moreover, TA3 inhibited the expression of various genes encoding anti-apoptotic (Bcl-2, Bcl-xl), proliferative (Cyclin D1), metastatic (MMP-9), and angiogenic (VEGF-1) proteins.

CONCLUSION

The results indicated that TA3, an active phytochemical from A. asphodeloides, could induce apoptosis and suppress cell proliferation by inhibiting the STAT3 and ERK1/2 pathways. Thus, TA3 is a candidate cancer chemotherapeutic agent instead to treat human pancreatic cancer.

Effect of BIS depletion on HSF1-dependent transcriptional activation in A549 non-small cell lung cancer cells

The expression of BCL-2 interacting cell death suppressor (BIS), an anti-stress or anti-apoptotic protein, has been shown to be regulated at the transcriptional level by heat shock factor 1 (HSF1) upon various stresses. Recently, HSF1 was also shown to bind to BIS, but the significance of these protein-protein interactions on HSF1 activity has not been fully defined. In the present study, we observed that complete depletion of BIS using a CRISPR/Cas9 system in A549 non-small cell lung cancer did not affect the induction of heat shock protein (HSP) 70 and HSP27 mRNAs under various stress conditions such as heat shock, proteotoxic stress, and oxidative stress. The lack of a functional association of BIS with HSF1 activity was also demonstrated by transient downregulation of BIS by siRNA in A549 and U87 glioblastoma cells. Endogenous BIS mRNA levels were significantly suppressed in BIS knockout (KO) A549 cells compared to BIS wild type (WT) A549 cells at the constitutive and inducible levels. The promoter activities of BIS and HSP70 as well as the degradation rate of BIS mRNA were not influenced by depletion of BIS. In addition, the expression levels of the mutant BIS construct, in which 14 bp were deleted as in BIS-KO A549 cells, were not different from those of the WT BIS construct, indicating that mRNA stability was not the mechanism for autoregulation of BIS. Our results suggested that BIS was not required for HSF1 activity, but was required for its own expression, which involved an HSF1-independent pathway.

KRIBB11 accelerates Mcl-1 degradation through an HSF1-independent, Mule-dependent pathway in A549 non-small cell lung cancer cells

The Bcl-2 family protein, Mcl-1 is known to have anti-apoptotic functions, and depletion of Mcl-1 by cellular stresses favors the apoptotic process. Moreover, Mcl-1 levels are frequently increased in various cancer cells, including non-small cell lung cancer (NSCLC), and is implicated in resistance to conventional chemotherapy and in cancer metastasis. In this study, we demonstrated that KRIBB11 accelerates the proteasomal degradation of Mcl-1 in the NSCLC cell line, A549. While KRIBB11 is an inhibitor of HSF1, we found that KRIBB11 induced Mcl-1 degradation in an HSF1-independent manner. Furthermore, this process was triggered via increase ubiquitination by the E3 ligase, Mule, rather than via de-ubiquitination by USP9X. Additionally, we found that Mcl-1 levels were only transiently reduced by KRIBB11: Mcl-1 levels were gradually restored as KRIBB11 activity diminished. However, we found that this effect was blocked in BIS (Bcl-2 interacting cell death suppressor, also called BAG3)-depleted cells, and that BIS prevents Mcl-1 from undergoing HSP70-driven proteasomal degradation, through an interaction with HSP70. Taken together, our results suggest that targeting Mcl-1 with KRIBB11 treatment, while simultaneously downregulating BIS, could be a therapeutic strategy in NSCLC.