A basal cell defect promotes budding of prostatic intraepithelial neoplasia.

Basal cells in a simple secretory epithelium adhere to the ECM, providing contextual cues for ordered repopulation of the luminal cell layer. Early high-grade prostatic intraepithelial neoplasia (HG-PIN) has enlarged nuclei/nucleoli, luminal layer expansion and genomic instability. Additional HG-PIN markers include loss of α6β4 integrin or its ligand, laminin-332, and budding of tumor clusters into laminin-511 rich stroma. We modeled the invasive budding phenotype by reducing expression of α6β4 integrin in spheroids formed from two normal human, stable isogenic prostate epithelial cell lines (RWPE-1 and PrEC 11220). Normal cells continuously spin in culture forming multicellular spheroids containing an outer laminin-332 layer, basal cells (expressing α6β4 integrin, high molecular weight cytokeratin, p63), and luminal cells that secrete PSA. Basal cells were optimally positioned relative to the laminin-332 layer as determined by spindle orientation. β4 defective spheroids contained a discontinuous laminin-332 layer corresponding to regions of abnormal budding. The 3D model can be readily used to study mechanisms that disrupt laminin-332 continuity, e.g. defects of the essential adhesion receptor (β4 integrin), laminin-332 or abnormal luminal expansion during HG-PIN progression.