CASP4 and colon carcinoma: CASP4 and CASP5 proteins are constitutively expressed in monocytes, unlike the low basal expression of CASP11 in murine macrophages.73 In human HT-29 colon carcinoma cells, IFNγ upregulated mRNA levels of CASP1 and CASP5, but not CASP4; however, CASP5 protein levels were not increased.