Caspase-14 is an anti-apoptotic protein targeting apoptosis-inducing factor in lung adenocarcinomas.

Using apoptosis-inducing factor protein as bait in a yeast hybrid assay to screen protein libraries, we identified three proteins that interacted with apoptosis-inducing factor: human homolog of yeast Rad23 protein A (hHR23A), microsomal glutathione S-transferase and caspase-14 (casp-14). In this study, we investigated the expression and function of casp-14 in lung adenocarcinomas (LADC). Our results showed that monoclonal antibodies were specific to casp-14, and that casp-14 was highly expressed in LADC. Casp-14 overexpression correlated with tumor stage, cell differentiation and lymphovascular involvement, suggesting that casp-14 was associated with tumor cell growth and metastatic potential. In vitro, casp-14 interacted with apoptosis-inducing factor, and silencing of casp-14 expression reduced cisplatin resistance. Our data suggest that casp-14 is an anti-apoptotic protein targeting apoptosis-inducing factor and increases cisplatin resistance in LADC cells.

Purification and characterization of active caspase-14 from human epidermis and development of the cleavage site-directed antibody.

Restricted expression of caspase-14 in differentiating keratinocytes suggests the involvement of caspase-14 in terminal differentiation. We purified active caspase-14 from human cornified cells with sequential chromatographic procedures. Specific activity increased 764-fold with a yield of 9.1%. Purified caspase-14 revealed the highest activity on WEHD-methylcoumaryl-amide (MCA), although YVAD-MCA, another caspase-1 substrate, was poorly hydrolyzed. The purified protein was a heterodimer with 17 and 11 kDa subunits. N-terminal and C-terminal analyses demonstrated that the large subunit consisted of Ser(6)-Asp(146) and N-terminal of small subunit was identified as Lys(153). We successfully developed an antiserum (anti-h14D146) directed against the Asp(146) cleavage site, which reacted only with active caspase-14 but not with procaspase-14. Furthermore we confirmed that anti-h14D146 did not show any reactivity to the active forms of other caspases. Immunohistochemical analysis demonstrated that anti-h14D146 staining was mostly restricted to the cornified layer and co-localized with some of the TUNEL positive-granular cells in the normal human epidermis. UV radiation study demonstrated that caspase-3 was activated and co-localized with TUNEL-positive cells in the middle layer of human epidermis. In contrast, we could not detect caspase-14 activation in response to UV. Our study revealed tightly regulated action of caspase-14, in which only the terminal differentiation of keratinocytes controls its activation process.