A heterochromatin gene signature unveils HP1α mediating neuroendocrine prostate cancer development and aggressiveness

Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer (PCa) with hyperchromatic nuclei being a distinguishing histopathological feature. Here we show that, underlying this distinct nuclear structure, heterochromatin related genes are significantly enriched in NEPC. Among them, heterochromatin protein 1α (HP1α) expression is increased early in NE transdifferentiation and is consistently elevated in clinical NEPC samples. Functional studies showed that HP1α knockdown attenuates NEPC tumor growth by inhibiting proliferation and survival. Its ectopic expression significantly promotes NE transdifferentiation in adenocarcinoma cells subjected to androgen deprivation treatment. To identify mechanisms underlying the function of HP1α involved in NEPC cell proliferation and adenocarcinoma cell NE transdifferentiation, we analyzed gene expression profiles from stable NEPC cell lines with control or HP1α knockdown, and adenocarcinoma cell lines with control or HP1α overexpression, respectively. NCI-H660 cell was transduced with lentiviral particles delivering control or HP1α shRNA. V16D cell was transduced with lentiviral particles delivering control or HP1α overexpressing plasmid. To induce neuroendocrine phenotype in V16D cell, cells were starved with phenol-red free RPMI-1640 containing 10% Charcoal-Stripped Serum for 24 hours, then cultured with the addition of 10 μM enzalutamide. Total RNA was extracted from stable cell lines, and applied for gene expression profiling analysis using Agilent SurePrint G3 Human Gene Expression v3 8x60K array.