KPNB1 inhibition disrupts proteostasis and triggers unfolded protein response-mediated apoptosis in glioblastoma cells

Abstract

The nuclear import receptor karyopherin β1 (KPNB1) is involved in the nuclear import of most proteins and in the regulation of multiple mitotic events. Upregulation of KPNB1 has been observed in cancers including glioblastoma. Depletion of KPNB1 induces mitotic arrest and apoptosis in cancer cells, but the underlying mechanism is not clearly elucidated. Here, we found that downregulation and functional inhibition of KPNB1 in glioblastoma cells induced growth arrest and apoptosis without apparent mitotic arrest. KPNB1 inhibition upregulated Puma and Noxa and freed Mcl-1-sequestered Bax and Bak, leading to mitochondrial outer membrane permeabilization (MOMP) and apoptosis. Moreover, combination of Bcl-xL inhibitors and KPNB1 inhibition enhanced apoptosis in glioblastoma cells. KPNB1 inhibition promoted cytosolic retention of its cargo and impaired cellular proteostasis, resulting in elevated polyubiquitination, formation of aggresome-like-induced structure (ALIS), and unfolded protein response (UPR). Ubiquitination elevation and UPR activation in KPNB1-deficient cells were reversed by KPNB1 overexpression or inhibitors of protein synthesis but aggravated by inhibitors of autophagy-lysosome or proteasome, indicating that rebalance of cytosolic/nuclear protein distribution and alleviation of protein overload favor proteostasis and cell survival. Chronic activation of eIF2α/ATF4 cascade of UPR was responsible for the upregulation of Puma and Noxa, apoptosis and ABT-263 sensitivity. Taken together, our findings demonstrate that KPNB1 is required for proteostasis maintenance and its inhibition induces apoptosis in glioblastoma cells through UPR-mediated deregulation of Bcl-2 family members.

Disease-specific alteration of karyopherin-α subtype establishes feed-forward oncogenic signaling in head and neck squamous cell carcinoma

“…The loss of function assay revealed that KPNA4-mediated nuclear transport is required for HNSCC proliferation. Recent studies demonstrated that certain karyopherins are elevated in several cancers and can regulate malignant phenotypes by affecting cytoplasmnuclear transport systems [25,[30][31][32][33][34]. Taken together, these results indicate that targeting disease-specifically altered transport systems may serve as promising therapeutic strategies for cancer treatment.…”

Defining the ATPome reveals cross-optimization of metabolic pathways

“…Notable CRISRPi basal ATP hits included eukaryotic translation initiation factor 4 (EIF4G2), whose knockdown decreases mitochondrial gene expression in embryonic stem cells 55 . RAN, the highest CRISPRi basal hit, and KPNB1, a low ATP basal hit whose inhibition disrupts mitochondrial function and leads to cell death, both function in protein import to the nucleus 56 , demonstrating a potentially nuanced link between nuclear protein import and mitochondrial function. Overall, there were also relatively few low ATP basal hits.…”

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

“…In mouse pancreatic acinar cells, cadmium chloride- or hyperosmotic sucrose-stimulated autophagy was found to be inhibited by cycloheximide [467], which likely inhibits autophagy at the segregation step. Cycloheximide is used to prevent the autophagy-lysosome pathway [468] and its effects can be rapidly reversed by its removal [469].…”