p16INK4A Represses the paracrine tumor-promoting effects of breast stromal fibroblasts

Abstract

Cancer-associated fibroblasts (CAFs), the most abundant and probably the most active cellular component of breast cancer-associated stroma, promote carcinogenesis through paracrine effects; however, the molecular basis remains elusive. We have shown here that p16INK4A expression is reduced in 83% CAFs as compared with their normal adjacent counterparts cancer-free tissues isolated from the same patients. This decrease is mainly due to AUF1-dependent higher turnover of the CDKN2A mRNA in CAFs. Importantly, p16INK4A downregulation using specific siRNA activated breast fibroblasts and increased the expression/secretion levels of stromal cell-derived factor 1 (SDF-1) and matrix metalloproteinase (MMP)-2. Consequently, media conditioned with these cells stimulated the proliferation of epithelial cells. Furthermore, the migration/invasion of breast cancer cells was also enhanced in an SDF-1-dependent manner. This effect was mediated through inducing an epithelial–mesenchymal transition state. By contrast, increase in p16INK4A level through ectopic expression or AUF1 downregulation, reduced the secreted levels of SDF-1 and MMP-2 and suppressed the pro-carcinogenic effects of CAFs. In addition, p16INK4A-defective fibroblasts accelerated breast tumor xenograft formation and growth rate in mice. Importantly, tumors formed in the presence of p16INK4A-defective fibroblasts exhibited higher levels of active Akt, Cox-2, MMP-2 and MMP-9, showing their greater aggressiveness as compared with xenografts formed in the presence of p16INK4A-proficient fibroblasts. These results provide the first indication that p16INK4A downregulation in breast stromal fibroblasts is an important step toward their activation.

The Cytokine IL-6 Reactivates Breast Stromal Fibroblasts through Transcription Factor STAT3-dependent Up-regulation of the RNA-binding Protein AUF1

“…This corroborates our recent findings showing that most human cancer-associated fibroblasts have reduced levels of p16 and that specific p16 downregulation increases the expression of ␣-SMA and SDF-1 and activates breast stromal fibroblasts (28). Similar findings were reported for p53 and p21 (29,(42)(43)(44), indicating that downregulation of these tumor suppressor genes is an important step toward the activation of stromal fibroblasts.…”

“…(hereafter referred to as p16) is reduced in active cancer-associated fibroblasts and that p16 down-regulation plays a major role in the activation of breast stromal fibroblasts (28). In the present report, we sought to determine the molecules and pathways that underlie the paracrine effects of breast cancer cells on stromal fibroblasts, leading to their activation and the downregulation of p16, p21, and p53.…”

Cancer-associated fibroblasts: A multifaceted driver of breast cancer progression

“…mCAFs, especially those isolated from the interface zone of breast tumors, are claimed to be a robust inducer of EMT [94,95]. With respect to the molecular mechanism, many mediators, such as Twist1 [96], SDF-1 [97] and the SNAIL family [51], were identified. Cycloxygenase-2 (COX-2)/nuclear factor-kappa B (NFκB)/hypoxiainducible factor-1 (HIF-1) signaling, and TGFβ, ERK, JUN and RHO signaling are thought to be responsible for mCAF-induced EMT [68,94,95,[98][99][100].…”

Obesity and p16INK4A Downregulation Activate Breast Adipocytes and Promote Their Protumorigenicity

“…Furthermore, p16 has antiinflammatory functions in rheumatoid synovial fibroblasts in vitro (44,45). Moreover, we have recently shown that p16 represses the expression/secretion of IL-6 in breast stromal fibroblasts (10).…”

“…In breast stromal fibroblasts, it has been shown that tumor suppressor genes, such as p16 INK4A (p16), play major roles in repressing the expression/secretion of several cancer-promoting cytokines (10).…”