V-ATPase-associated prorenin receptor is upregulated in prostate cancer after PTEN loss

Phosphatase and tensin homolog (PTEN) tumor suppressor protein loss is common in prostate cancer (PCa). PTEN loss increases PI3K/Akt signaling, which promotes cell growth and survival. To find secreted biomarkers of PTEN loss, a proteomic screen was used to compare secretomes of cells with and without PTEN expression. We showed that PTEN downregulates Prorenin Receptor (PRR) expression and secretion of soluble Prorenin Receptor (sPRR) in PCa cells and in mouse. PRR is an accessory protein required for assembly of the vacuolar ATPase (V-ATPase) complex. V-ATPase is required for lysosomal acidification, amino acid sensing, efficient mechanistic target of Rapamycin complex 1 (mTORC1) activation, and β-Catenin signaling. On PCa tissue microarrays, PRR expression displayed a positive correlation with Akt phosphorylation. Moreover, PRR expression was required for proliferation of PCa cells by maintaining V-ATPase function. Further, we provided evidence for a potential clinical role for PRR expression and sPRR concentration in differentiating low from high Gleason grade PCa. Overall, the current study unveils a mechanism by which PTEN can inhibit tumor growth. Lower levels of PRR result in attenuated V-ATPase activity and reduced PCa cell proliferation.

WISP1 is associated to advanced disease, EMT and an inflamed tumor microenvironment in multiple solid tumors

Background: WNT1-Inducible Signaling Pathway Protein 1 (WISP1) is implicated in prostate cancer growth and metastasis and the regulation of inflammation in diverse benign diseases. The objectives of this study were to assess the prognostic value of WISP1, its association to inflammation and its relevance as a biomarker for immune checkpoint blockade (ICB) response. Methods: Publicly available RNA-seq datasets were used to evaluate the prognostic value of WISP1 gene expression and its association with tumor-infiltrating lymphocytes, inflamed tumor microenvironment, and anti-PD-1 ICB response. A tissue microarray (TMA) including 285 radical prostatectomy specimens was used to confirm these associations in prostate cancer. The effect of recombinant WISP1 (rWISP1) on inflammatory cytokines was assessed in vitro. Results: High levels of WISP1 correlated with BCR-free survival in prostate adenocarcinoma and overall survival in primary melanoma, low-grade glioma, and kidney papillary cell carcinoma. Some effects could be accounted for by higher WISP1 expression in advanced disease. High WISP1 expression in prostate adenocarcinoma was correlated with CD8+ cells density. In vitro, rWISP1 increased inflammatory cytokine production. High WISP1 gene expression in RNA-seq datasets was correlated with gene signatures of multiple immune cell types as well as an inflammatory cytokine, immune checkpoint, and epithelial-mesenchymal transition (EMT) gene expression. WISP1 mRNA expression was associated with primary resistance to ICB in datasets showing EMT. Conclusions: Our results support an association between WISP1 expression and advanced disease, EMT and an inflamed tumor microenvironment in multiple solid tumors. The consequences of WISP1 expression on cancer immunotherapy remains to be addressed.

Abstract 2654: Immunologic and prognostic correlates of WISP1 in prostate cancer

Background: Avoidance of immune destruction and tumor-promoting inflammation are equally important cancer hallmarks. In the context of prostate cancer, inflammatory markers and high levels of immune infiltrates have been associated with shorter biochemical recurrence (BCR)-free survival. WNT1 Inducible Signaling Pathway (WISP1) has been implicated in prostate cancer metastasis and the regulation of inflammation in diverse benign diseases. Thus, the objectives of this study were: 1) to assess the prognostic value of WISP1 in human prostate cancer, and 2) to determine the association of WISP1 to the inflammatory landscape specific to this disease.

Methods: A tumor microarray (TMA) was constructed with radical prostatectomy specimens of 285 prostate cancer patients. Multicolor manual immunofluorescence (IF) was performed to simultaneously detect WISP1, CD8 and cytokeratins 8 and 18. WISP1 expression levels were determined by the mean fluorescence intensity (MFI) in stromal, epithelial, cytoplasmic and nuclear (DAPI) areas in each core, and CD8+ cell density was determined for each compartment by dividing cell count by the percentage of the core occupied by the compartment. Finally, the prostate cancer TCGA dataset (n = 548) was used to validate the prognostic value of WISP1 mRNA expression, as well as its association to CD8+ lymphocytes using previously validated gene signatures (Becht et al., 2016).

Results: IF analyses of our TMA revealed that high levels of WISP1 in normal adjacent epithelium are significantly associated with shorter BCR-free survival in Kaplan-Meier (log-rank = 4.246, p = 0.039) and univariate Cox regression analyses (hazard ratio = 1.477; p = 0.042), but not in multivariate Cox regression analyses (hazard ratio = 1.381; p = 0.101). Furthermore, a significant correlation was found between WISP1 expression and CD8+ cell density. Gene expression analyses further showed that WISP1-high prostate tumors are associated with a CD8+ lymphocyte gene enrichment profile, and confirmed that patients with WISP1-high prostate tumors have reduced BCR-free survival (Wilcoxon rank, p = 0.003).

Conclusions: Overall, our results support a negative prognostic association for WISP1 as well as a proinflammatory role. WISP1 may represent a relevant target for the improvement of prostate cancer immunotherapy.

Citation Format: Pierre-Olivier Gaudreau, Sylvie Clairefond, Pierre-Luc Boulay, Pavel Chrobak, Bertrand Allard, Sandra Pommey, Fred Saad, Marian Young, John Stagg. Immunologic and prognostic correlates of WISP1 in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2654.

Rab11-FIP1C Is a Critical Negative Regulator in ErbB2-Mediated Mammary Tumor Progression

Rab coupling protein (FIP1C), an effector of the Rab11 GTPases, including Rab25, is amplified and overexpressed in 10% to 25% of primary breast cancers and correlates with poor clinical outcome. Rab25 is also frequently silenced in triple-negative breast cancer, suggesting its ability to function as either an oncogene or a tumor suppressor, depending on the breast cancer subtype. However, the pathobiologic role of FIP family members, such as FIP1C, in a tumor-specific setting remains elusive. In this study, we used ErbB2 mouse models of human breast cancer to investigate FIP1C function in tumorigenesis. Doxycycline-induced expression of FIP1C in the MMTV-ErbB2 mouse model resulted in delayed mammary tumor progression. Conversely, targeted deletion of FIP1C in the mammary epithelium of an ErbB2 model coexpressing Cre recombinase led to accelerated tumor onset. Genetic and biochemical characterization of these FIP1C-proficient and -deficient tumor models revealed that FIP1C regulated E-cadherin (CDH1) trafficking and ZONAB (YBX3) function in Cdk4-mediated cell-cycle progression. Furthermore, we demonstrate that FIP1C promoted lysosomal degradation of ErbB2. Consistent with our findings in the mouse, the expression of FIP1C was inversely correlated with ErbB2 levels in breast cancer patients. Taken together, our findings indicate that FIP1C acts as a tumor suppressor in the context of ErbB2-positive breast cancer and may be therapeutically exploited as an alternative strategy for targeting aberrant ErbB2 expression. Cancer Res; 76(9); 2662-74. ©2016 AACR.

Vascular endothelial growth factor receptor-2 activates ADP-ribosylation factor 1 to promote endothelial nitric-oxide synthase activation and nitric oxide release from endothelial cells

Vascular endothelial growth factor (VEGF) induces angiogenesis and regulates endothelial function via production and release of nitric oxide (NO), an important signaling molecule. The molecular basis leading to NO production involves phosphatidylinositiol-3 kinase (PI3K), Akt, and endothelial nitric-oxide synthase (eNOS) activation. In this study, we have examined whether small GTP-binding proteins of the ADP-ribosylation factor (ARF) family act as molecular switches to regulate signaling cascades activated by VEGF in endothelial cells. Our results show that this growth factor can promote the rapid and transient activation of ARF1. In endothelial cells, this GTPase is present on dynamic plasma membrane ruffles. Inhibition of ARF1 expression, using RNA interference, markedly impaired VEGF-dependent eNOS phosphorylation and NO production by preventing the activation of the PI3K/Akt signaling axis. Furthermore, our data indicate that phosphorylation of Tyr(801), on VEGF receptor 2, is essential for activating Src- and ARF1-dependent signaling events leading to NO release from endothelial cells. Lastly, this mediator is known to regulate a broad variety of endothelial cell functions. Depletion of ARF1 markedly inhibits VEGF-dependent increase of vascular permeability as well as capillary tubule formation, a process important for angiogenesis. Taken together, our data indicate that ARF1 is a novel modulator of VEGF-stimulated NO release and signaling in endothelial cells.

ADP-ribosylation factor 1 controls the activation of the phosphatidylinositol 3-kinase pathway to regulate epidermal growth factor-dependent growth and migration of breast cancer cells

Activation of intracellular signaling pathways by growth factors is one of the major causes of cancer development and progression. Recent studies have demonstrated that monomeric G proteins of the Ras family are key regulators of cell proliferation, migration, and invasion. Using an invasive breast cancer cell lines, we demonstrate that the ADP-ribosylation factor 1 (ARF1), a small GTPase classically associated with the Golgi, is an important regulator of the biological effects induced by epidermal growth factor. Here, we show that this ARF isoform is activated following epidermal growth factor stimulation and that, in MDA-MB-231 cells, ARF1 is found in dynamic plasma membrane ruffles. Inhibition of endogenous ARF1 expression results in the inhibition of breast cancer cell migration and proliferation. The underlying mechanism involves the activation of the phosphatidylinositol 3-kinase pathway. Our data demonstrate that depletion of ARF1 markedly impairs the recruitment of the phosphatidylinositol 3-kinase catalytic subunit (p110alpha) to the plasma membrane, and the association of the regulatory subunit (p85alpha) to the activated receptor. These results uncover a novel molecular mechanism by which ARF1 regulates breast cancer cell growth and invasion during cancer progression.

Endogenous ARF6 interacts with Rac1 upon angiotensin II stimulation to regulate membrane ruffling and cell migration

ARF6 and Rac1 are small GTPases known to regulate remodelling of the actin cytoskeleton. Here, we demonstrate that these monomeric G proteins are sequentially activated when HEK 293 cells expressing the angiotensin type 1 receptor (AT(1)R) are stimulated with angiotensin II (Ang II). After receptor activation, ARF6 and Rac1 transiently form a complex. Their association is, at least in part, direct and dependent on the nature of the nucleotide bound to both small G proteins. ARF6-GTP preferentially interacts with Rac1-GDP. AT(1)R expressing HEK293 cells ruffle, form membrane protrusions, and migrate in response to agonist treatment. ARF6, but not ARF1, depletion using small interfering RNAs recapitulates the ruffling and migratory phenotype observed after Ang II treatment. These results suggest that ARF6 depletion or Ang II treatment are functionally equivalent and point to a role for endogenous ARF6 as an inhibitor of Rac1 activity. Taken together, our findings reveal a novel function of endogenously expressed ARF6 and demonstrate that by interacting with Rac1, this small GTPase is a central regulator of the signaling pathways leading to actin remodeling.

G protein-coupled receptor endocytosis in ADP-ribosylation factor 6-depleted cells

The internalization of G protein-coupled receptors is regulated by several important proteins that act in concert to finely control this complex cellular process. Here, we have applied the RNA interference approach to demonstrate that ADP-ribosylation factor 6 (ARF6) is essential for the endocytosis of a broad variety of receptors. Reduction of endogenous expression of ARF6 in HEK 293 cells resulted in a correlated inhibition of the beta(2) -adrenergic receptor internalization previously characterized as being sequestered via the clathrin-coated vesicle pathway. Furthermore, other receptors internalizing via this endocytic route, namely the angiotensin type 1 receptor and the vasopressin type 2 receptor, were also impaired in their ability to be sequestered when levels of endogenous ARF6 in cells were reduced. Interestingly, endocytosis of the endothelin type B receptor, characterized as being internalized via the caveolae pathway, was also markedly inhibited in ARF6-depleted cells. In contrast, internalization of the vasoactive intestinal peptide receptor was unaffected by reduced levels of ARF6. Finally, internalization of the acetylcholine-muscarinic type 2 receptor via the non-clathrin-coated vesicle pathway was also inhibited in ARF6-depleted cells. Taken together, our results demonstrate that ARF6 proteins play an essential role in the internalization process of most G protein-coupled receptors regardless of the endocytic route being utilized. However, this phenomenon is not general. In some cases, another ARF isoform or other proteins may be essential to regulate the endocytic process.