CRACD loss promotes small cell lung cancer tumorigenesis via EZH2-mediated immune evasion.

ABSTRACT

The mechanisms underlying immune evasion and immunotherapy resistance in small cell lung cancer (SCLC) remain unclear. Herein, we investigate the role of CRACD tumor suppressor in SCLC. We found that CRACD is frequently inactivated in SCLC, and Cracd knockout (KO) significantly accelerates SCLC development driven by loss of Rb1, Trp53, and Rbl2. Notably, the Cracd-deficient SCLC tumors display CD8+ T cell depletion and suppression of antigen presentation pathway. Mechanistically, CRACD loss silences the MHC-I pathway through EZH2. EZH2 blockade is sufficient to restore the MHC-I pathway and inhibit CRACD loss-associated SCLC tumorigenesis. Unsupervised single-cell transcriptomic analysis identifies SCLC patient tumors with concomitant inactivation of CRACD, impairment of tumor antigen presentation, and downregulation of EZH2 target genes. Our findings define CRACD loss as a new molecular signature associated with immune evasion of SCLC cells and proposed EZH2 blockade as a viable option for CRACD-negative SCLC treatment.