Abstract
Caspases play an important role in maintaining tissue homeostasis. Active Caspase-6 (Casp6) is considered a novel therapeutic target against Alzheimer disease (AD) since it is present in AD pathological brain lesions, associated with age-dependent cognitive decline, and causes age-dependent cognitive impairment in the mouse brain. However, active Casp6 is highly expressed and activated in normal human colon epithelial cells raising concerns that inhibiting Casp6 in AD may promote colon carcinogenesis. Furthermore, others have reported rare mutations of Casp6 in human colorectal cancers and an effect of Casp6 on apoptosis and metastasis of colon cancer cell lines. Here, we investigated the role of Casp6 in inflammation-associated azoxymethane/dextran sulfate sodium (AOM/DSS) colon cancer in Casp6-overexpressing and -deficient mice. In wild-type mice, AOM/DSS-induced tumors had significantly higher Casp6 mRNA, protein and activity levels compared to normal adjacent colon tissues. Increased human Casp6 or absence of Casp6 expression in mice colon epithelial cells did not change colonic tumor multiplicity, burden or distribution. Nevertheless, the incidence of hyperplasia was slightly reduced in human Casp6-overexpressing colons and increased in Casp6 null colons. Overexpression of Casp6 did not affect the grade of the tumors while all tumors in heterozygous or homozygous Casp6 null colons were high grade compared to only 50% high grade in wild-type mice. Casp6 levels did not alter cellular proliferation and apoptosis. These results suggest that Casp6 is unlikely to be involved in colitis-associated tumors.
Highlights
Caspases are a family of intracellular cysteine proteases that play an important role in tissue homeostasis through modulation of inflammation and apoptosis
Casp6 activity was confirmed in tumors but not in normal tissue by the detection of laminDA cleaved by Casp6 since lamin A is the prototypical substrate of Casp6 [39](Fig. 1E)
These results indicate that Casp6 mRNA, protein and activity levels are increased in AOM/dextran sodium sulfate (DSS)-induced colon tumors
Summary
Caspases are a family of intracellular cysteine proteases that play an important role in tissue homeostasis through modulation of inflammation and apoptosis. Dysregulation of these proteases result in inflammatory disorders, neurodegenerative diseases, and cancer [1]. Casp has been implicated in both Huntington and Parkinson’s disease [18, 19]. Together, these findings suggest that inhibition of Casp might be an efficient therapeutic approach against neurodegenerative diseases including cognitive decline in aged and AD individuals
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