A PTP1B-Cdk3 Signaling Axis Promotes Cell Cycle Progression of Human Glioblastoma Cells through an Rb-E2F Dependent Pathway

PTP1B plays a key role in developing different types of cancer. However, the molecular mechanism underlying this effect is unclear. To identify molecular targets of PTP1B that mediate its role in tumorigenesis, we undertook a SILAC-based phosphoproteomic approach, which allowed us to identify Cdk3 as a novel PTP1B substrate. Substrate trapping experiments and docking studies revealed stable interactions between the PTP1B catalytic domain and Cdk3. In addition, we observed that PTP1B dephosphorylates Cdk3 at tyrosine residue 15 in vitro and interacts with it in human glioblastoma cells. Next, we found that pharmacological inhibition of PTP1B or its depletion with siRNA leads to cell cycle arrest with diminished activity of Cdk3, hypophosphorylation of Rb, and the downregulation of E2F target genes Cdk1, Cyclin A, and Cyclin E1. Finally, we observed that the expression of a constitutively active Cdk3 mutant bypasses the requirement of PTP1B for cell cycle progression and expression of E2F target genes. These data delineate a novel signaling pathway from PTP1B to Cdk3 required for efficient cell cycle progression in an Rb-E2F dependent manner in human GB cells.

Mexican Colorectal Cancer Research Consortium (MEX-CCRC): Etiology, Diagnosis/Prognosis, and Innovative Therapies

In 2013, recognizing that Colorectal Cancer (CRC) is the second leading cause of death by cancer worldwide and that it was a neglected disease increasing rapidly in Mexico, the community of researchers at the Biomedicine Research Unit of the Facultad de Estudios Superiores Iztacala from the Universidad Nacional Autónoma de México (UNAM) established an intramural consortium that involves a multidisciplinary group of researchers, technicians, and postgraduate students to contribute to the understanding of this pathology in Mexico. This article is about the work developed by the Mexican Colorectal Cancer Research Consortium (MEX-CCRC): how the Consortium was created, its members, and its short- and long-term goals. Moreover, it is a narrative of the accomplishments of this project. Finally, we reflect on possible strategies against CRC in Mexico and contrast all the data presented with another international strategy to prevent and treat CRC. We believe that the Consortium's characteristics must be maintained to initiate a national strategy, and the reported data could be useful to establish future collaborations with other countries in Latin America and the world.

p21-Activated Kinase 1 Promotes Breast Tumorigenesis via Phosphorylation and Activation of the Calcium/Calmodulin-Dependent Protein Kinase II

p21-Activated kinase-1 (Pak1) is frequently overexpressed and/or amplified in human breast cancer and is necessary for transformation of mammary epithelial cells. Here, we show that Pak1 interacts with and phosphorylates the Calcium/Calmodulin-dependent Protein Kinase II (CaMKII), and that pharmacological inhibition or depletion of Pak1 leads to diminished activity of CaMKII. We found a strong correlation between Pak1 and CaMKII expression in human breast cancer samples, and combined inhibition of Pak1 and CaMKII with small-molecule inhibitors was synergistic and induced apoptosis more potently in Her2 positive and triple negative breast cancer (TNBC) cells. Co-adminstration of Pak and CaMKII small-molecule inhibitors resulted in a dramatic reduction of proliferation and an increase in apoptosis in a 3D cell culture setting, as well as an impairment in migration and invasion of TNBC cells. Finally, mice bearing xenografts of TNBC cells showed a significant delay in tumor growth when treated with small-molecule inhibitors of Pak and CaMKII. These data delineate a signaling pathway from Pak1 to CaMKII that is required for efficient proliferation, migration and invasion of mammary epithelial cells, and suggest new therapeutic strategies in breast cancer.

LPA1 Receptor Promotes Progesterone Receptor Phosphorylation through PKCα in Human Glioblastoma Cells

Lysophosphatidic acid (LPA) induces a wide range of cellular processes and its signaling is increased in several cancers including glioblastoma (GBM), a high-grade astrocytoma, which is the most common malignant brain tumor. LPA1 receptor is expressed in GBM cells and its signaling pathways activate protein kinases C (PKCs). A downstream target of PKC, involved in GBM progression, is the intracellular progesterone receptor (PR), which can be phosphorylated by this enzyme, increasing its transcriptional activity. Interestingly, in GBM cells, PKCα isotype translocates to the nucleus after LPA stimulation, resulting in an increase in PR phosphorylation. In this study, we determined that LPA1 receptor activation induces protein-protein interaction between PKCα and PR in human GBM cells; this interaction increased PR phosphorylation in serine400. Moreover, LPA treatment augmented VEGF transcription, a known PR target. This effect was blocked by the PR selective modulator RU486; also, the activation of LPA1/PR signaling promoted migration of GBM cells. Interestingly, using TCGA data base, we found that mRNA expression of LPAR1 increases according to tumor malignancy and correlates with a lower survival in grade III astrocytomas. These results suggest that LPA1/PR pathway regulates GBM progression.

IFI27/ISG12 Downregulates Estrogen Receptor α Transactivation by Facilitating Its Interaction With CRM1/XPO1 in Breast Cancer Cells

The estrogen receptor alpha (ERα) is a ligand-activated transcription factor whose activity is modulated by its interaction with multiple protein complexes. In this work, we have identified the protein interferon alpha inducible protein 27 (IFI27/ISG12) as a novel ERα-associated protein. IFI27/ISG12 transcription is regulated by interferon and estradiol and its overexpression is associated to reduced overall survival in ER+ breast cancer patients but its function in mammary gland tissue remains elusive. In this study we showed that overexpression of IFI27/ISG12 in breast cancer cells attenuates ERα transactivation activity and the expression of ERα-dependent genes. Our results demonstrated that IFI27/ISG12 overexpression in MCF-7 cells reduced their proliferation rate in 2-D and 3-D cell culture assays and impaired their ability to migrate in a wound-healing assay. We show that IFI27/ISG12 downregulation of ERα transactivation activity is mediated by its ability to facilitate the interaction between ERα and CRM1/XPO1 that mediates the nuclear export of large macromolecules to the cytoplasm. IFI27/ISG12 overexpression was shown to impair the estradiol-dependent proliferation and tamoxifen-induced apoptosis in breast cancer cells. Our results suggest that IFI27/ISG12 may be an important factor in regulating ERα activity in breast cancer cells by modifying its nuclear versus cytoplasmic protein levels. We propose that IFI27/ISG12 may be a potential target of future strategies to control the growth and proliferation of ERα-positive breast cancer tumors.

Helminth-derived molecules inhibit colitis-associated colon cancer development through NF-κB and STAT3 regulation

Inflammation is currently considered a hallmark of cancer and plays a decisive role in different stages of tumorigenesis, including initiation, promotion, progression, metastasis and resistance to antitumor therapies. Colorectal cancer is a disease widely associated with local chronic inflammation. Additionally, extrinsic factors such as infection may beneficially or detrimentally alter cancer progression. Several reports have noted the ability of various parasitic infections to modulate cancer development, favoring tumor progression in many cases and inhibiting tumorigenesis in others. The aim of our study was to determine the effects of excreted/secreted products of the helminth Taenia crassiceps (TcES) as a treatment in a murine model of colitis-associated colon cancer (CAC). Here, we found that after inducing CAC, treatment with TcES was able to reduce inflammatory cytokines such as IL-1β, TNF-α, IL-33 and IL-17 and significantly attenuate colon tumorigenesis. This effect was associated with the inhibition of signal transducer and activator of transcription 3 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) phosphorylation. Furthermore, we determined that TcES interfered with LPS-induced NF-κB p65 activation in human colonic epithelial cell lines in a Raf-1 proto-oncogene-dependent manner. Moreover, in three-dimensional cultures, TcES promoted reorganization of the actin cytoskeleton, altering cell morphology and forming colonospheres, features associated with a low grade of aggressiveness. Our study demonstrates a remarkable effect of helminth-derived molecules on suppressing ongoing colorectal cancer by downregulating proinflammatory and protumorigenic signaling pathways.

p21 Activated kinase 1: Nuclear activity and its role during DNA damage repair

p21-activated kinase 1 (PAK1) is a serine/threonine kinase activated by the small GTPases Rac1 and Cdc42. It is located in the chromosome 11q13 and is amplified and/or overexpressed in several human cancer types including 25-30% of breast tumors. This enzyme plays a pivotal role in the control of a number of fundamental cellular processes by phosphorylating its downstream substrates. In addition to its role in the cytoplasm, it is well documented that PAK1 also plays crucial roles in the nucleus participating in mitotic events and gene expression through its association and/or phosphorylation of several transcription factors, transcriptional co-regulators and cell cycle-related proteins, including Aurora kinase A (AURKA), polo-like kinase 1 (PLK1), the forkhead transcription factor (FKHR), estrogen receptor α (ERα), and Snail. More recently, PAK signaling has emerged as a component of the DNA damage response (DDR) as PAK1 activity influences the cellular sensitivity to ionizing radiation and promotes the expression of several genes involved in the Fanconi Anemia/BRCA pathway. This review will focus on the nuclear functions of PAK1 and its role in the regulation of DNA damage repair.

Abstract 1876: Reduced Pak1 activity sensitizes FA/BRCA-proficient breast cancer cells to PARP inhibition

Cells that are deficient in homologous recombination, such as those that have mutations in any of the Fanconi Anemia (FA)/BRCA pathway genes, are hypersensitive to inhibition of poly(ADP-ribose) polymerase (PARP). However, FA/BRCA-deficient tumors represent only a small fraction of breast cancers, which might restrict the therapeutic utility of PARP inhibitor monotherapy. p21-activated kinase 1 (Pak1) is a serine/threonine protein kinase located in the chromosome 11q13 and is amplified and/or overexpressed in several human cancer types including 25-30% of breast tumors. This enzyme controls many cellular processes by phosphorylating its downstream substrates; in addition to its role in the cytoplasm, Pak1 also affects gene transcription due to its nuclear localization and association with chromatin. It is now recognized that Pak1 activation is a component of the DNA damage response. Here, we show that depletion or inhibition of Pak1 down-regulated the expression of several genes involved in the FA/BRCA pathway and compromised the ability of cells to repair DNA by homologous recombination, induced cell cycle arrest, promoted apoptosis and resulted in reduced colony formation. Combined inhibition of Pak1 and PARP in pak1 amplified breast cancer cells had a synergistic effect, enhanced apoptosis, resulted in reduced colony formation and delayed tumor growth in a xenograft setting. Inhibition of Pak1 did not sensitize non-transformed or Pak1 non-amplified cells to inhibition of PARP. Because reduced Pak1 activity impaired FA/BRCA function and consequently, repair by homologous recombination, inhibition of this kinase in pak1 amplified and/or overexpressing breast cancer cells represents a plausible strategy for expanding the utility of PARP inhibitors to FA/BRCA-proficient cancers.

Citation Format: Olga Villamar-Cruz, Tatiana Prudnikova, Neil Johnson, Jonathan Chernoff, Luis E. Arias Romero. Reduced Pak1 activity sensitizes FA/BRCA-proficient breast cancer cells to PARP inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1876.

Abstract A02: Pak1 kinase inhibition sensitizes 11q13 amplified breast cancer cells to platinum based chemotherapy via downregulation of Fanconi anemia genes

Activating mutations in Ras GTPases frequently occur in many types of human cancers but are rarely detected in breast tumors. However, activation of the Ras/Raf/MEK/ERK pathway is commonly observed in human breast cancers, suggesting that other genetic alterations lead to activation of this signaling pathway. Several studies have shown that signaling through the Ras/Raf/MEK/ERK pathway can be influenced by Pak1 kinase, a downstream effector of the Ras-related C3 botulinum toxin substrate 1 (Rac1) GTPase. In addition, it has been shown that Pak1 is amplified in several human cancer types, including 25-30% of breast tumor samples and cancer cell lines, and that its kinase activity is necessary for Ras mediated transformation.

In this work, we performed a comparative gene profiling study in order to identify differentially regulated genes between wild-type and Pak1 deficient mouse and human breast cancer cells. Several genes involved in the Fanconi Anemia/BRCA pathway - a DNA-damage response signaling pathway that is essential for repairing DNA interstrand cross-links induced by DNA-damaging agents like cisplatin and doxorubicin - were down-regulated in Pak1 deficient cells. The reduced expression of FANCD2 and FANCI was confirmed by qPCR and western blot in Pak1-depleted human breast cancer cells with or without 11q13 amplification. Interestingly, the depletion or chemical inhibition of Pak1 in 11q13 amplified breast cancer cells treated with cisplatin, compromised the ability of these cells to repair DNA by homologous recombination, induced cell cycle arrest, promoted apoptosis and resulted in reduced colony formation. In contrast, the inhibition or depletion of Pak1 had little effect on these cellular processes in Pak1-non-amplified breast cancer cells.

Because reduced Pak1 activity impaired Fanconi Anemia/BRCA signaling and consequently, repair by homologous recombination, inhibition of Pak1 represents a plausible strategy for expanding the utility of DNA-damaging treatments to Fanconi Anemia/BRCA-proficient 11q13 amplified breast cancers.

Citation Format: Luis E. Arias-Romero, Olga Villamar-Cruz, Jonathan Chernoff. Pak1 kinase inhibition sensitizes 11q13 amplified breast cancer cells to platinum based chemotherapy via downregulation of Fanconi anemia genes. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A02. doi: 10.1158/1557-3125.RASONC14-A02

Abstract B31: Pak1 and β-catenin inhibition blocks tumor progression in ErbB2-driven breast cancer models

p21-activated kinase-1 (Pak1) is frequently upregulated in human breast cancer and is required for transformation of mammary epithelial cells by ErbB2. However, its role in tumorigenesis in vivo, and the particular signaling pathways affected, are not defined.

In this work, we examined the distinct roles of Pak1 and Pak2 in cellular and animal models of ErbB2-driven breast cancer. We found that inhibition of Pak1, but not Pak2, impedes transformation by ErbB2 in a 3D cell culture system, but that loss of either Pak1 or Pak2 causes loss of both Erk and Akt activation. A phospho-proteomic screen revealed that Pak1-deficient, but not Pak2-deficient, ErbB2 cells showed almost total loss of β-catenin expression that is accompanied by a significant reduction in almost all known β-catenin target genes. In MMTV-ErbB2 transgenic mice, loss of Pak1 prolonged survival, and mammary tissues of such mice showed loss of β-catenin. Expression of a β-catenin mutant bearing a phospho-mimetic mutation at Ser 675, a specific Pak1 phosphorylation site, restored the ability of ErbB2 to transform Pak1-deficient mammary epithelial cells. Lastly, we showed that small molecule inhibitors of Pak or β-catenin blocked transformation by ErbB2 in 3D culture and tumorigenesis by ErbB2 in mouse xenografts, and combined inhibition by both agents was synergistic. These findings establish Pak1 as a new target in ErbB2-driven breast cancer and define a new mechanism of action primarily through the β-catenin, but not the Erk or Akt, signaling pathways.

Citation Format: Luis E. Arias-Romero, Olga Villamar-Cruz, Jonathan Chernoff. Pak1 and β-catenin inhibition blocks tumor progression in ErbB2-driven breast cancer models. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B31.

Pak1 kinase links ErbB2 to β-catenin in transformation of breast epithelial cells

p21-Activated kinase-1 (Pak1) is frequently upregulated in human breast cancer and is required for transformation of mammary epithelial cells by ErbB2. Here, we show that loss of Pak1, but not the closely related Pak2, leads to diminished expression of β-catenin and its target genes. In MMTV-ErbB2 transgenic mice, loss of Pak1 prolonged survival, and mammary tissues of such mice showed loss of β-catenin. Expression of a β-catenin mutant bearing a phospho-mimetic mutation at Ser 675, a specific Pak1 phosphorylation site, restored transformation to ErbB2-positive, Pak1-deficient mammary epithelial cells. Mice bearing xenografts of ErbB2-positive breast cancer cells showed tumor regression when treated with small-molecule inhibitors of Pak or β-catenin, and combined inhibition by both agents was synergistic. These data delineate a signaling pathway from ErbB2 to Pak to β-catenin that is required for efficient transformation of mammary epithelial cells, and suggest new therapeutic strategies in ErbB2-positive breast cancer.

Activation of Src by protein tyrosine phosphatase 1B Is required for ErbB2 transformation of human breast epithelial cells

Protein tyrosine phosphatase (PTP) 1B plays a major role in inhibiting signaling from the insulin and leptin receptors. Recently, PTP1B was found to have an unexpected positive role in ErbB2 signaling in a mouse model of breast cancer, but the mechanism underlying this effect has been unclear. Using human breast epithelial cells grown in a three-dimensional matrix, we found that PTP1B, but not the closely related enzyme T-cell PTP, is required for ErbB2 transformation in vitro. Activation of ErbB2, but not ErbB1, increases PTP1B expression, and increased expression of PTP1B activates Src and induces a Src-dependent transformed phenotype. These findings identify a molecular mechanism by which PTP1B links an important oncogenic receptor tyrosine kinase to signaling pathways that promote aberrant cell division and survival in human breast epithelial cells.

Regulation of the content of progesterone and estrogen receptors, and their cofactors SRC-1 and SMRT by the 26S proteasome in the rat brain during the estrous cycle

In this work we have determined the role of the 26S proteasome in the regulation of the content of progesterone receptors (PR-A and PR-B), estrogen receptors (ER-alpha and ER-beta), the coactivator SRC-1 and the corepressor SMRT in the rat brain during the estrous cycle. The 26S proteasome inhibitor MG132 was injected once into the lateral ventricle on proestrous day; and 24h later, on estrous day we evaluated the content of PR and ER isoforms, SRC-1 and SMRT in the hypothalamus, the preoptic area and the hippocampus by Western blot. A significant increase in the content of both PR isoforms, ER-beta and SRC-1 was observed after the administration of MG132 in the three studied cerebral regions. SMRT content was increased in the hypothalamus and the preoptic area and a significant increase in ER-alpha content was only observed in the preoptic area. These results suggest that essential proteins that participate in progesterone and estrogen actions in the brain should be regulated by the 26S proteasome in a tissue-specific manner in physiological conditions.

Changes in progesterone receptor isoforms content in the rat brain during the oestrous cycle and after oestradiol and progesterone treatments

We studied the effects of oestradiol and progesterone on progesterone receptor (PR) isoform content in the brain of ovariectomized rats and in intact rats during the oestrous cycle by Western blot analysis. In the hypothalamus and the preoptic area of ovariectomized rats, PR-A and PR-B content was increased by oestradiol, whereas progesterone significantly diminished the content of both PR isoforms after 3 h of treatment in the hypothalamus, but not in the preoptic area. In the hippocampus, only PR-A content was significantly increased by oestradiol while progesterone significantly diminished it after 12 h of treatment. In the frontal cortex, no treatment significantly modified PR isoform content. During the oestrous cycle, the lowest content of PR isoforms in the hypothalamus was observed on diestrus day and, by contrast, in the preoptic area, the highest content of both PR isoforms was observed on diestrus day. We observed no changes in PR isoform content in the hippocampus during the oestrous cycle. These results indicate that the expression of PR isoforms is differentially regulated by sex steroid hormones in a regionally specific manner.

Regulation of progesterone receptor isoforms expression by sex steroids in the rat lung

In this work, we determined the expression pattern and the hormonal regulation of progesterone receptor (PR) isoforms in the rat lung of ovariectomized female rats after estradiol (E2) and progesterone (P4) treatments. We also evaluated the content of estrogen receptor beta (ER-beta) which is the ER isoform expressed in the lung. RNA and proteins were extracted and processed for reverse transcription (RT) coupled to polymerase chain reaction (PCR) and Western blot, respectively. The expression of both PR isoforms in the lung at mRNA and at protein levels was up-regulated by E2 while P4 down-regulated it at mRNA level. P4 did not modify PR isoforms protein content unlike its effect in the uterus where both PR isoforms were down-regulated by their ligand at mRNA and protein levels. PR-A was the predominant isoform, both in the lung and in the uterus. In the lung, ER-beta was down-regulated by E2 while P4 did not significantly modify the effect of E2. These results suggest that both PR isoforms should be expressed in the rat lung, and that their expression should be differentially regulated at mRNA and at protein levels by P4. We also suggest that the up-regulation of PR isoforms by E2 in the lung is mediated by ER-beta.

Participation of the 26S proteasome in the regulation of progesterone receptor concentrations in the rat brain

The aim of this study was to investigate the participation of the 26S proteasome in the regulation of progesterone receptor (PR) concentrations in the rat brain in vivo. Ovariectomized adult female rats were treated with estradiol (10 microg/100 g s.c.), estradiol + progesterone (400 microg/100 g), and vehicle (corn oil/10% ethanol) in the presence or absence of the proteasome inhibitor Z-Ile-Glu (OBu(1))-Ala-Leu-H (PSI, 300 microg/100 g). Proteins were extracted from the preoptic area, the hippocampus, and the frontal cortex, and processed for Western blot. Estradiol-induced PR expression in the preoptic area and the hippocampus, whereas progesterone did not modify the effect of estradiol. Neither estradiol nor progesterone modified PR content in the frontal cortex. PSI treatment increased PR content in the preoptic area and the hippocampus. This increase was significant in both regions after 24 h of the treatment with progesterone + PSI in the animals primed with estradiol. In this case, the content of both PR isoforms (PR-A and PR-B) was increased in a similar manner by PSI in the preoptic area (90 and 97%) and in the hippocampus (49 and 50%). PSI did not affect PR content in the frontal cortex. Our results suggest that the 26S proteasome could participate in the turnover of PR in the preoptic area and the hippocampus of the rat in vivo.