Cell-autonomous induction of functional tumor suppressor 15-lipoxygenase 2 (15-LOX2) contributes to replicative senescence of human prostate progenitor cells

Abstract

Normal human prostatic (NHP) epithelial cells undergo senescence in vitro and in vivo, but little is known about the tissue-specific molecular mechanisms. Here we first characterize young primary NHP cells as CK5 þ /CK18 þ intermediate basal cells that also express several other putative stem/progenitor cell markers including p63, CD44, a2b1, and hTERT. When cultured in serum-and androgen-free medium, NHP cells gradually lose the expression of these markers, slow down in proliferation, and enter senescence. Several pieces of evidence implicate 15-lipoxygenase 2 (15-LOX2), a molecule with a restricted tissue expression and most abundantly expressed in adult human prostate, in the replicative senescence of NHP cells. First, the 15-LOX2 promoter activity and the mRNA and protein levels of 15-LOX2 and its multiple splice variants are upregulated in serially passaged NHP cells, which precede replicative senescence and occur in a cell-autonomous manner. Second, all immortalized prostate epithelial cells and prostate cancer cells do not express 15-LOX2. Third, PCa cells stably transfected with 15-LOX2 or 15-LOX2sv-b, a splice variant that does not possess arachidonate-metabolizing activity, show a passage-related senescence-like phenotype. Fourth, infection of early-passage NHP cells with retroviral vectors encoding 15-LOX2 or 15-LOX2sv-b induces partial cellcycle arrest and big and flat senescence-like phenotype. Finally, 15-LOX2 protein expression in human prostate correlates with age. Together, these data suggest that 15-LOX2 may represent an endogenous prostate senescence gene and its tumor-suppressing functions might be associated with its ability to induce cell senescence.

Differential androgen receptor signals in different cells explain why androgen-deprivation therapy of prostate cancer fails

“…The consequence of increased apoptosis in luminal cells and increased proliferation in basal intermediate cells then resulted in less differentiated yet larger primary tumors in the ventral prostate of pes-ARKO-TRAMP mice than tumors from 16-week-old TRAMP mice (Niu et al, 2008b). The primary prostate tumors of pes-ARKO-TRAMP mice exhibited a higher population of CD44-positive (Liu et al, 2004;Bhatia et al, 2005) and CK5/CK8-positive (van Leenders and Schalken, 2003;Bhatia et al, 2005) intermediate-like cells than those found in wild-type TRAMP mice (Niu et al, 2008a). Incidentally, CD44-positive, but ARnegative prostate cancer cells purified from human prostate cancer xenografts were also enriched in tumorigenic and metastatic progenitor cells (Patrawala et al, 2006).…”

Highly purified CD44+ prostate cancer cells from xenograft human tumors are enriched in tumorigenic and metastatic progenitor cells

“…Basal cells express cytokeratin 5 (CK5), CK14, Bcl-2 (McDonnell et al, 1992), Her-2/neu (Reiter and Sawyers, 2001), p63 (Signoretti et al, 2000), and CD44 (Liu et al, 1997), whereas differentiated luminal cells express CK8, CK18, AR (androgen receptor), prostate-specific antigen (PSA), prostatic acid phosphatase (PAP), CD57, and 15-lipoxygenase 2 (Tang et al, 2002;Bhatia et al, 2005). The basal cell compartment is thought to contain stem/ progenitor cells as >80% of the proliferating cells are localized in the basal layer (Bonkhoff et al, 1994).…”

Synergistic effect of 15-lipoxygenase 2 and radiation in killing head-and-neck cancer

“…33 Tang et al 21 reported that 15S-HETE at non-physiologically high concentrations (X25 mM) induces apoptosis in prostate cancer cells, but in the presence of exogenous AA, the 15-LOX-2 stable clones showed a significant increase in apoptosis. 22 Most recently, Subbarayan et al 34 found that a relatively low concentration of 15S-HETE (1 or 5 mM) was sufficient for PPARg activation in the presence, but not in the absence of 15-LOX-2 expression, in epithelial cells and cancer cells of prostate. We showed significant induction of apoptosis by restored expression of 15-LOX-2 (in the presence of exogenous AA) in the HNC cells transfected with the 15-LOX-2 expression vector (Figure 4).…”

“…Understanding nuclear targeting of 15-LOX-2 might conceptually provide an explanation to the tumor suppressing function of 15-LOX-2. The previous study 22 claimed that one 15-LOX-2 splice variant (15-LOX2sv-b) inhibits tumor growth of prostate cancer cells, but has reduced nuclear targeting and/or no AA metabolizing activity. It is noted that this variant contains a deletion of two exons.…”

“…Moreover, 15-LOX-2 was found to be a negative cell-cycle regulator in normal epithelial cells 21 and may be associated with the ability to induce cell senescence. 22 All together, 15-LOX-2 plays an anticarcinogenic role in many epithelia-derived carcinomas including HNC.…”