NRG1 and breast carcinoma: Interestingly, some NRG1 isoforms contain putative nuclear targeting sequences (Holmes et al., 1992), that translocate to the nucleus and alter gene expression as shown for the type I NRG1 isoform heregulin β1, whose translocation generates proapoptotic effects in breast cancer cells (Li et al., 1996; Weinstein and Leder, 2000) and for cysteine-rich domain isoforms of NRG1 in sensory neurons of mice spinal ganglia (Bao et al., 2003).