Publication Date


Document Type


Committee Members

Michael G. Kemp, Ph.D. (Advisor); Ravi P. Sahu, Ph.D. (Committee Member); Yong-Jie Xu, M.D., Ph.D. (Committee Member)

Degree Name

Master of Science (MS)


Cathepsin L is a lysosomal cysteine protease that is encoded by the CTSL gene in humans. Previous results have shown that CTSL expression and activity towards the DNA repair protein XPA are elevated in lysates of confluent/quiescent HaCaT keratinocytes. Because other nuclear proteins, including 53BP1 and histone H3, have also been reported to be CTSL substrates under conditions of cell differentiation, senescence, or quiescence, CTSL expression and activity (cleavage) of multiple nuclear proteins was examined in lysates from HaCaT cells and other cell lines at various days after plating and cell confluency. Our study found that adding CTSL inhibitors to a cell lysis buffer will block the artifactual cleavage of these nuclear proteins during cell lysis, which calls into question the interpretation of several previous publications. Furthermore, CTSL levels in human sera have been reported to display circadian rhythmicity, and we found that expression of CTSL in confluent cells can by controlled by clock modulating compounds. Specifically, we found that the REV-ERB antagonist SR8278 and the ROR agonist SR1078 cause a decrease in CTSL levels in a manner independent of the core clock protein BMAL1. These results provide greater insight into CTSL activity and regulation by the circadian clock.

Page Count


Department or Program

Department of Pharmacology and Toxicology

Year Degree Awarded