CREB5 as an essential transcription and tumorigenic regulator in basal-like breast and prostate cancer.
Authors: Makovec Allison , Tape Sydney , Bergom Hannah E. , Richter Camden , Deacon Aiden , Ali Atef Mir , Rennhack Jonathan , Ludwig Megan , Antonarakis Emmanuel S. , Drake Justin , Hwang Justin 
Published: June 2024

1107 Background: Breast cancers (BC) harbor basal-like transcriptional profiles, in which a large subset are pathologically triple negative breast cancers (TNBC). These are hormone therapy insensitive, have limited targeted therapies, and decreased overall survival (OS). Recent studies determined that prostate cancers (PCs) also exhibit luminal- or basal-like transcriptional subtypes. The 30-40% of basal-like PCs exhibit resistance to hormone therapies and have overall worse clinical outcomes. Here we deployed in silico computational models and tumor phenotype testing in vitro and in vivo. This identified that CREB5, a transcription factor commonly amplified or overexpressed in advanced cancers, regulates basal-like BCs and PCs through stem cell-like genes and properties that drive tumor formation. Methods: Protein and RNA levels were examined in 5 subtypes of BC from the TCGA (n=981). Normalized expression and PAM50 signatures were analyzed using data from Decipher tests of PC patients (n=585). Kaplan-Meier curves were used to compare relapse free survival in PC (n=84) and OS in TNBC (n=248). The ALAN (Algorithm for Linking Activity Networks (1) computational tool was used to determine gene-gene similarities of ~20,000 genes based on ~400,000,000 pairwise comparisons in 208 tumors. In PC (LNCaP) and TNBC (MDA-MB-231 and HCC1806) cell lines, we examined gene expression profiles from RNA-seq and found Hallmark signatures through Gene Set Enrichment Analysis. Motif analysis was conducted from ChIP-seq data on immuno-precipitated CREB5. We conducted in vitro and in vivo assessment of tumorigenicity. Results: Basal BCs harbored increased CREB5 expression and CREB5-high basal BCs had worse outcomes (HR 2.09, 95% CI 1.1-3.96, p<0.021). Reflecting this, in basal-like BC cell lines, CREB5 increased cell viability and formation of tumor-like spheroids in 3D culture. In PCs, CREB5 had a positive correlation with basal- and not luminal-like PCs (Spearman ρ = 0.519, p<0.001). Through ALAN analysis of metastatic PCs, CREB5 exhibited strong concordance with other known resistance genes (FGFR1/2) as well as transcription factors that promote stem cell-like features. Particularly, CREB5 was associated with increased FOSL1 (Spearman ρ = 0.37, p<0.001), a metastasis-regulating gene. In PC cell lines, CREB5 overexpression promoted FOSL1 and other stem cell-like genes and co-bound to FOSL1 transcription regulatory elements. CREB5 overexpression in PC cell lines promoted the formation of tumor-like colonies, spheroids, and increased tumor formation from the xenografts in mice. Conclusions: Basal-like BCs and PCs demonstrate overexpression of CREB5, a gene that promotes tumor formation and stem cell-like genes. This mechanistic knowledge may guide treatment management strategies and aid in the development of novel therapies against basal-like BCs and PCs. 1. Bergom et al, Communications Biology, 2023.