Role of Proprotein Convertases in Prostate Cancer Progression

Abstract

Better understanding of the distinct and redundant functions of the proprotein convertase (PC) enzyme family within pathophysiological states has a great importance for potential therapeutic strategies. In this study, we investigated the functional redundancy of PCs in prostate cancer in the commonly used androgen-sensitive LNCaP and the androgen-independent DU145 human cell lines. Using a lentiviral-based shRNA delivery system, we examined in vitro and in vivo cell proliferation characteristics of knockdown cell lines for the endogenous PCs furin, PACE4, and PC7 in both cell lines. Of the three PCs, only PACE4 was essential to maintain a high-proliferative status, as determined in vitro using XTT proliferation assays and in vivo using tumor xenografts in nude mice. Furin knockdowns in both cell lines had no effects on cell proliferation or tumor xenograft growth. Paradoxically, PC7 knockdowns reduced in vitro cellular proliferation but had no effect in vivo. Because PCs act within secretion pathways, we showed that conditioned media derived from PACE4 knockdown cells had very poor cell growth-stimulating effects in vitro. Immunohistochemistry of PACE4 knockdown tumors revealed reduced Ki67 and higher p27(KIP) levels (proliferation and cell cycle arrest markers, respectively). Interestingly, we determined that the epidermal growth factor receptor signaling pathway was activated in PC7 knockdown tumors only, providing some explanations of the paradoxical effects of PC7 silencing in prostate cancer cell lines. We conclude that PACE4 has a distinct role in maintaining proliferation and tumor progression in prostate cancer and this positions PACE4 as a relevant therapeutic target for this disease.

PACE4 Undergoes an Oncogenic Alternative Splicing Switch in Cancer

“…S7I and S7J). These results demonstrate the distinct functions of the two isoforms in sustaining cancer cell growth, in which PACE4-altCT plays a much more important role, allowing the conclusion that (i) the PACE4 knockdown-associated phenotype in prostate cancer cells (7) results from the downregulation of PACE4-altCT ( Supplementary Fig. S7B) and (ii) efficacy of PACE4 inhibitors and cell permeability requirements are in fact due to PACE4-altCT-specific functions.…”

“…Mycoplasma testing was done routinely (after every new cryotube thawing). Stable knockdown cell lines were the same as reported by Couture and colleagues (7). Stably expressing cell lines were never passaged more than 15 times.…”

“…In prostate cancer, among other PCs, PACE4 is specifically overexpressed and carries nonredundant growth-sustaining functions for cancer cells (6,7). PACE4 inhibition using either silencing tools or the high affinity PACE4 inhibitor: [dL]LLLRVK-amidinobenzylamide (Amba) herein called C23, both prevented prostate cancer tumor progression (8).…”

PCSK6 regulated by LH inhibits the apoptosis of human granulosa cells via activin A and TGFβ2

“…PCSK6 was found to be essential for maintaining a high proliferative state in prostate cancer cell lines (Couture et al 2012). Activin A and TGFb2 were believed to be proapoptosis factors in various tissue and cell types such as murine adrenal X-zone (Beuschlein et al 2003), intestinal mucosa (Dunker et al 2002), trophoblast cells (Yu et al 2012), granulosa cells (Quezada et al 2012), oligodendrocytes (Quezada et al 2012), hepatocytes (Hughes & Evans 2003), and endometrial stromal cells (Moulton 1994).…”

Structure-Based Optimization of a Potent PACE4 Inhibitor Containing a Decarboxylated P1 Arginine Mimetic

“…Our recent studies have provided direct evidence for the critical role of PACE4 in the progression of prostrate cancer, identifying this enzyme as a promising target to design novel and effective treatments [1]. Moreover, we developed a potent PACE4 inhibitor with considerable selectivity (20-fold over furin) known as the Multi-Leu (ML) peptide [2].…”