A tight balance of Karyopherin β1 expression is required in cervical cancer cells

KPNB1-mediated nuclear import in cancer

Dysregulation of nucleocytoplasmic shuttling impairs cellular homeostasis and promotes cancer development. KPNB1 is a member of karyopherin β family, mediating the transportation of proteins from the cytoplasm to the nucleus. In a variety of cancers, the expression of KPNB1 is upregulated to facilitate tumor growth and progression. Both downregulation of KPNB1 level and inhibition of KPNB1 activity prevent the entry of cancer-related transcription factors into the nucleus, subsequently suppressing the proliferation and metastasis of cancer cells. Currently, five KPNB1 inhibitors have been reported and exhibited good efficacy against cancer. This paper provides an overview of the role and mechanism of KPNB1 in different cancers and KPNB1-targeted anticancer compounds which hold promise for the future.

Expression of Karyopherin Alpha 2 and Karyopherin Beta 1 Correlate with Poor Prognosis in Gastric Cancer

INTRODUCTION

Karyopherin alpha 2 (KPNA2) and karyopherin beta 1 (KPNB1) constitute nuclear transport protein complexes involved in nuclear import and are significant in tumor progression. Although high KPNA2 expression was associated with poor prognosis in solid tumors, the relationship between KPNA2 and KPNB1 expression and their prognostic role in gastric cancer (GC) remains unclear.

METHODS

Immunohistochemistry was used to correlate the expression of KPNA2 and KPNB1 with various features, including clinicopathological characteristics in 130 patients with GC and survival in 94 patients with invasive lesions extending to the submucosa or deeper.

RESULTS

High expression of KPNA2 and KPNB1 was found in 25% and 36% of the patients, respectively. Both were significantly related to tumor depth, lymph node metastasis, lymphatic invasion, venous invasion, and Ki-67 expression. KPNA2 expression was significantly related to that of KPNB1 (p < 0.001). Patients with high KPNB1 expression had poorer prognosis than those with low expression (p = 0.027), as was also observed in case of KPNA2 (p < 0.001). Patients with high expression of both KPNA2 and KPNB1 accounted for 18% and had a poorer prognosis than those with high expression of either and those with low expression of both (p = 0.001). Multivariate analysis revealed that high expression of both KPNA2 and KPNB1 was an independent prognostic factor in patients with GC (hazard ratio, 3.46; 95% confidence interval, 1.64-2.73, p = 0.001).

CONCLUSION

KPNA2 expression was correlated with KPNB1 expression, and high co-expression of KPNA2 and KPNB1 may represent a strong prognostic biomarker in GC.

A mass spectrometry-based approach for the identification of Kpnβ1 binding partners in cancer cells

Karyopherin beta 1 (Kpnβ1) is the principal nuclear importer of cargo proteins and plays a role in many cellular processes. Its expression is upregulated in cancer and essential for cancer cell viability, thus the identification of its binding partners might help in the discovery of anti-cancer therapeutic targets and cancer biomarkers. Herein, we applied immunoprecipitation coupled to mass spectrometry (IP-MS) to identify Kpnβ1 binding partners in normal and cancer cells. IP-MS identified 100 potential Kpnβ1 binding partners in non-cancer hTERT-RPE1, 179 in HeLa cervical cancer, 147 in WHCO5 oesophageal cancer and 176 in KYSE30 oesophageal cancer cells, including expected and novel interaction partners. 38 binding proteins were identified in all cell lines, with the majority involved in RNA metabolism. 18 binding proteins were unique to the cancer cells, with many involved in protein translation. Western blot analysis validated the interaction of known and novel binding partners with Kpnβ1 and revealed enriched interactions between Kpnβ1 and select proteins in cancer cells, including proteins involved in cancer development, such as Kpnα2, Ran, CRM1, CCAR1 and FUBP1. Together, this study shows that Kpnβ1 interacts with numerous proteins, and its enhanced interaction with certain proteins in cancer cells likely contributes to the cancer state.

Recognition motifs for importin 4 [(L)PPRS(G/P)P] and importin 5 [KP(K/Y)LV] binding, identified by bio-informatic simulation and experimental in vitro validation

Nuclear translocation of large proteins is mediated through karyopherins, carrier proteins recognizing specific motifs of cargo proteins, known as nuclear localization signals (NLS). However, only few NLS signals have been reported until now. In the present work, NLS signals for Importins 4 and 5 were identified through an unsupervised in silico approach, followed by experimental in vitro validation. The sequences LPPRS(G/P)P and KP(K/Y)LV were identified and are proposed as recognition motifs for Importins 4 and 5 binding, respectively. They are involved in the trafficking of important proteins into the nucleus. These sequences were validated in the breast cancer cell line T47D, which expresses both Importins 4 and 5. Elucidating the complex relationships of the nuclear transporters and their cargo proteins is very important in better understanding the mechanism of nuclear transport of proteins and laying the foundation for the development of novel therapeutics, targeting specific importins.

Novel small molecule inhibitor of Kpnβ1 induces cell cycle arrest and apoptosis in cancer cells

Karyopherin beta 1 (Kpnβ1) is a major nuclear import receptor that mediates the import of cellular cargoes into the nucleus. Recently it has been shown that Kpnβ1 is highly expressed in several cancers, and its inhibition by siRNA induces apoptotic cancer cell death, while having little effect on non-cancer cells. This study investigated the effect of a novel small molecule, Inhibitor of Nuclear Import-60 (INI-60), on cancer cell biology, as well as nuclear import activities associated with Kpnβ1, and cancer progression in vivo using cervical and oesophageal cancer cell lines. INI-60 treatment resulted in the inhibition of cancer cell proliferation, colony formation, migration and invasion, and induced a G1/S cell cycle arrest, followed by cancer cell death via apoptosis. Non-cancer cells were minimally affected by INI-60 at concentrations that inhibited cancer cells. INI-60 treatment altered the localisation of Kpnβ1 and its cargoes, NFκB/p65, NFAT and AP-1, and the overexpression of Kpnβ1 reduced INI-60 cytotoxicity. INI-60 also inhibited KYSE 30 oesophageal cancer cell line growth in vivo. Taken together, these results show that INI-60 inhibits the nuclear import of Kpnβ1 cargoes and interferes with cancer cell biology. INI-60 presents as a potential therapeutic approach for cancers of different tissue origins and warrants further investigation as a novel anti-cancer agent.

Inhibition of Kpnβ1 mediated nuclear import enhances cisplatin chemosensitivity in cervical cancer

Background

Inhibition of nuclear import via Karyopherin beta 1 (Kpnβ1) shows potential as an anti-cancer approach. This study investigated the use of nuclear import inhibitor, INI-43, in combination with cisplatin.

Methods

Cervical cancer cells were pre-treated with INI-43 before treatment with cisplatin, and MTT cell viability and apoptosis assays performed. Activity and localisation of p53 and NFκB was determined after co-treatment of cells.

Results

Pre-treatment of cervical cancer cells with INI-43 at sublethal concentrations enhanced cisplatin sensitivity, evident through decreased cell viability and enhanced apoptosis. Kpnβ1 knock-down cells similarly displayed increased sensitivity to cisplatin. Combination index determination using the Chou-Talalay method revealed that INI-43 and cisplatin engaged in synergistic interactions. p53 was found to be involved in the cell death response to combination treatment as its inhibition abolished the enhanced cell death observed. INI-43 pre-treatment resulted in moderately stabilized p53 and induced p53 reporter activity, which translated to increased p21 and decreased Mcl-1 upon cisplatin combination treatment. Furthermore, cisplatin treatment led to nuclear import of NFκB, which was diminished upon pre-treatment with INI-43. NFκB reporter activity and expression of NFκB transcriptional targets, cyclin D1, c-Myc and XIAP, showed decreased levels after combination treatment compared to single cisplatin treatment and this associated with enhanced DNA damage.

Conclusions

Taken together, this study shows that INI-43 pre-treatment significantly enhances cisplatin sensitivity in cervical cancer cells, mediated through stabilization of p53 and decreased nuclear import of NFκB. Hence this study suggests the possible synergistic use of nuclear import inhibition and cisplatin to treat cervical cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07819-3.

Inhibiting Importin 4-mediated nuclear import of CEBPD enhances chemosensitivity by repression of PRKDC-driven DNA damage repair in cervical cancer

Cervical cancer (CC) remains highest in the mortality of female reproductive system cancers, while cisplatin (CDDP) resistance is the one of main reasons for the lethality. Preceding evidence has supported that karyopherins are associated with chemoresistance. In this study, we simultaneously compared CDDP-incomplete responders with CDDP-complete responders of CC patients and CDDP‐insensitive CC cell lines with CDDP‐sensitive group. We finally identified that DNA-PKcs (PRKDC) was related to CDDP sensitivity after overlapping in CC sample tissues and CC cell lines. Further functional assay revealed that targeting PRKDC by shRNA and NU7026 (specific PRKDC inhibitor) could enhance CDDP sensitivity in vitro and in vivo, which was mediated by impairing DNA damage repair pathway in CC. Mechanistically, we found that PRKDC was transcriptionally upregulated by CCAAT/enhancer-binding protein delta (CEBPD), while intriguingly, CDDP treatment strengthened the transcriptional activity of CEBPD to PRKDC. We further disclosed that Importin 4 (IPO4) augmented the nuclear translocation of CEBPD through nuclear localization signals (NLS) to activate PRKDC-mediated DNA damage repair in response to CDDP. Moreover, we demonstrated that IPO4 and CEBPD knockdown improved CDDP-induced cytotoxicity in vitro and in vivo. Together, we shed the novel insight into the role of IPO4 in chemosensitivity and provide a clinical translational potential to enhance CC chemosensitivity since the IPO4-CEBPD-PRKDC axis is actionable via NU7026 (PRKDC inhibitor) or targeting IPO4 in combination with CDDP.