RESUMO
BACKGROUND: In the USA, the breast cancer mortality rate is 41% higher for African-American women than non-Hispanic White women. While numerous gene expression studies have classified biological features that vary by race and may contribute to poorer outcomes, few studies have experimentally tested these associations. CRYßB2 gene expression has drawn particular interest because of its association with overall survival and African-American ethnicity in multiple cancers. Several reports indicate that overexpression of the CRYßB2 pseudogene, CRYßB2P1, and not CRYßB2 is linked with race and poor outcome. It remains unclear whether either or both genes are linked to breast cancer outcomes. This study investigates CRYßB2 and CRYßB2P1 expression in human breast cancers and breast cancer cell line models, with the goal of elucidating the mechanistic contribution of CRYßB2 and CRYßB2P1 to racial disparities. METHODS: Custom scripts for CRYßB2 or CRYßB2P1 were generated and used to identify reads that uniquely aligned to either gene. Gene expression according to race and tumor subtype were assessed using all available TCGA breast cancer RNA sequencing alignment samples (n = 1221). In addition, triple-negative breast cancer models engineered to have each gene overexpressed or knocked out were developed and evaluated by in vitro, biochemical, and in vivo assays to identify biological functions. RESULTS: We provide evidence that CRYßB2P1 is expressed at higher levels in breast tumors compared to CRYßB2, but only CRYßB2P1 is significantly increased in African-American tumors relative to White American tumors. We show that independent of CRYßB2, CRYßB2P1 enhances tumorigenesis in vivo via promoting cell proliferation. Our data also reveal that CRYßB2P1 may function as a non-coding RNA to regulate CRYßB2 expression. A key observation is that the combined overexpression of both genes was found to suppress cell growth. CRYßB2 overexpression in triple-negative breast cancers increases invasive cellular behaviors, tumor growth, IL6 production, immune cell chemoattraction, and the expression of metastasis-associated genes. These data underscore that both CRYßB2 and CRYßB2P1 promote tumor growth, but their mechanisms for tumor promotion are likely distinct. CONCLUSIONS: Our findings provide novel data emphasizing the need to distinguish and study the biological effects of both CRYßB2 and CRYßB2P1 as both genes independently promote tumor progression. Our data demonstrate novel molecular mechanisms of two understudied, disparity-linked molecules.
