Int J Biol Sci 2022; 18(6):2362-2371. doi:10.7150/ijbs.70172 This issue

Research Paper

COVID-19 receptor and malignant cancers: Association of CTSL expression with susceptibility to SARS-CoV-2

Lianmei Zhang1,2,3#, Chunli Wei2#, Dabing Li2,4#, Jiayue He2#, Shuguang Liu2, Haoyue Deng2, Jingliang Cheng2, Jiaman Du2, Xiaoyan Liu2, Hanchun Chen5, Suan Sun3, Hong Yu1✉, Junjiang Fu2✉

1. Department of Pathology, Taizhou People's Hospital Affiliated to Nanjing University of Chinese Medicine, Taizhou, Jiangsu Province, China.
2. Key Laboratory of Epigenetics and Oncology, the Research Center for Preclinical Medicine, Southwest Medical University, Luzhou 646000, Sichuan Province, China.
3. Department of Pathology, The Affiliated Huaian No. 1 People's Hospital of Nanjing Medical University, Huai'an 223300, Jiangsu Province, China.
4. Basic Medical School, Southwest Medical University, Luzhou 646000, Sichuan Province, China.
5. Department of Biochemistry, School of Life Sciences, Central South University, Changsha 410013, Hunan Province, China.
#These authors contributed equally to this work.

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Zhang L, Wei C, Li D, He J, Liu S, Deng H, Cheng J, Du J, Liu X, Chen H, Sun S, Yu H, Fu J. COVID-19 receptor and malignant cancers: Association of CTSL expression with susceptibility to SARS-CoV-2. Int J Biol Sci 2022; 18(6):2362-2371. doi:10.7150/ijbs.70172. Available from

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Graphic abstract

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.

Keywords: The CTSL gene, Malignant cancers, SARS-Cov-2, COVID-19, Susceptibility, N6, N6-dimethyladenosine (m62A), Cordycepin (CD)