Ploidy-dependent change in cyclin D2 expression and sensitization to cdk4/6 inhibition in human somatic haploid cells

Fragility of ER homeostatic regulation underlies haploid instability in human somatic cells

Mammalian somatic cells are generally unstable in the haploid state, resulting in haploid-to-diploid conversion within a short time frame. However, cellular and molecular principles that limit the sustainability of somatic haploidy remain unknown. In this study, we found the haploidy-linked vulnerability to endoplasmic reticulum (ER) stress as a critical cause of haploid intolerance in human somatic cells. Pharmacological induction of ER stress selectively induced apoptosis in haploid cells, facilitating the replacement of haploids by coexisting diploidized cells in a caspase-dependent manner. Biochemical analyses revealed that unfolded protein response (UPR) was activated with similar dynamics between haploids and diploids upon ER stress induction. However, haploids were less efficient in solving proteotoxic stress, resulting in a bias toward a proapoptotic mode of UPR signaling. Artificial replenishment of chaperone function substantially alleviated the haploidy-linked upregulation of proapoptotic signaling and improved haploid cell retention under tunicamycin-induced ER stress. These data demonstrate that the ER stress-driven haploid instability stems from inefficient proteostatic control that alters the functionality of UPR to cause apoptosis selectively in haploids. Interestingly, haploids suffered a higher level of protein aggregation even in unperturbed conditions, and the long-term stability of the haploid state was significantly improved by alleviating their natural proteotoxicity. Based on these results, we propose that the haploidy-specific vulnerability to ER stress creates a fundamental cause of haploid intolerance in mammalian somatic cells. Our findings provide new insight into the principle that places a stringent restriction on the evolution of animal life cycles.

BHLHE41 promotes U87 and U251 cell proliferation via ERK/cyclinD1 signaling pathway

Purpose

The biological functions of BHLHE41 in the proliferation of glioblastoma remained unexplored. We aimed to investigate the biological roles and underlying molecular mechanisms of BHLHE41 in glioblastoma.

Materials and methods

We used multiple methods, including Western blot analysis, soft agar colony-formation assay, CCK8 assay, and flow cytometry, to evaluate the changes in multiple cellular functions after BHLHE41 knockdown or overexpression in U87 and U251 cell lines. The TCGA database was then used to analyze the associations between BHLHE41 expression with clinicopathological factors and the overall survival (OS) of glioma patients.

Results

This study determined that overexpression of BHLHE41 promoted glioma cell proliferation and colony formation. Besides, BHLHE41 upregulated cyclinD1, cyclinD3, and cyclinE1 expression and drove phase transition from G1 to S and G2 phases by upregulating these cyclins. In contrast, knockdown of BHLHE41 had an opposite effect on all of these parameters. However, BHLHE41 had no effect on apoptosis. Moreover, BHLHE41 activated MAPK/ERK signaling pathway to upregulate cyclinD1 expression. After the ERK signal pathway was blocked by a specific inhibitor, SCH772984, cyclinD1 upregulation was reversed. Furthermore, the median OS of low-grade glioma (LGG) patients with low to median level of BHLHE41 was 22.6 months, longer than that of the patients with high level of BHLHE41 (21.0 months).

Conclusion

BHLHE41 has an important role in the proliferation of glioblastoma and could serve as a novel candidate for targeted therapy of glioblastoma.