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Introduction: In the world, the incidence of breast cancer has surpassed that of lung cancer, and it has become the first malignant tumor among women. Triple-negative breast cancer (TNBC) shows an extremely heterogeneous malignancy toward high recurrence, metastasis, and mortality, but there is a lack of effective targeted therapy. It is urgent to develop novel molecular targets in the occurrence and therapeutics for TNBC, and novel therapeutic strategies to block the recurrence and metastasis of TNBC. Methods: In this study, CTSL (cathepsin L) expression in tissues and adjacent tissues of TNBC patients was monitored by immunohistochemistry and western blots. The correlations between CTSL expressions and clinicopathological characteristics in the patient tissues for TNBC were analyzed. Cell proliferation, migration, and invasion assay were also performed when over-expressed or knocked-down CTSL. Results: We found that the level of CTSL in TNBC is significantly higher than that in the matched adjacent tissues, and associated with differentiated degree, TNM Stage, tumor size, and lymph node metastatic status in TNBC patients. The high level of CTSL was correlated with a short RFS (p<0.001), OS (p<0.001), DMFS (p<0.001), PPS (p= 0.0025) in breast cancer from online databases; while in breast cancer with lymph node-positive, high level of CTSL was correlated with a short DMFS (p<0.001) and RFS (p<0.001). Moreover, in vitro experiments showed that CTSL overexpression promotes the abilities for proliferation, migration, and invasion in MCF-7 and MDA-MB-231 cell lines, while knocking-down CTSL decreases its characteristics in MDA-MB-231 cell lines. Conclusion: CTSL might involve into the regulation of the proliferation, invasion, and metastasis of TNBC. Thus, CTSL would be a novel, potential therapeutic, and prognostic target of TNBC.
RESUMO
CTSL is expressed by cancerous tissues and encodes a lysosomal cysteine proteinase that regulates cancer progression and SARS-CoV-2 entry. Therefore, it is critical to predict the susceptibility of cancer patients for SARS-CoV-2 and evaluate the correlation between disease outcomes and the expression of CTSL in malignant cancer tissues. In the current study, we analyzed CTSL expression, mutation rate, survival and COVID-19 disease outcomes in cancer and normal tissues, using online databases. We also performed immunohistochemistry (IHC) to test CTSL expression and western blot to monitor its regulation by cordycepin (CD), and N6, N6-dimethyladenosine (m62A), respectively. We found that CTSL is conserved across different species, and highly expressed in both normal and cancer tissues from human, as compared to ACE2 or other proteinases/proteases. Additionally, the expression of CTSL protein was the highest in the lung tissue. We show that the mRNA expression of CTSL is 66.4-fold higher in normal lungs and 54.8-fold higher in cancer tissues, as compared to ACE2 mRNA expression in the respective tissues. Compared to other proteases/proteinases/convertases such as TMPRSS2 and FURIN, the expression of CTSL was higher in both normal lungs and lung cancer samples. All these data indicate that CTSL might play an important role in COVID-19 pathogenesis in normal and cancer tissues of the lungs. Additionally, the CTSL-002 isoform containing both the inhibitor_I29 and Peptidase_C1 domains was highly prevalent in all cancers, suggesting its potential role in tumor progression and SARS-CoV-2 entry in multiple types of cancers. Further analysis of the expression of CTSL mutant showed a correlation with FURIN and TMPRSS2, suggesting a potential role of CTSL mutations in modulating SARS-CoV-2 entry in cancers. Moreover, high expression of CTSL significantly correlated with a short overall survival (OS) in lung cancer and glioma. Thus, CTSL might play a major role in the susceptibility of lung cancer and glioma patients to SARS-CoV-2 uptake and COVID-19 severity. Furthermore, CD or m62A inhibited CTSL expression in the cancer cell lines A549, MDA-MB-231, and/or PC3 in a dose dependent manner. In conclusion, we show that CTSL is highly expressed in normal tissues and increased in most cancers, and CD or m62A could inhibit its expression, suggesting the therapeutic potential of targeting CTSL for cancer and COVID-19 treatment.