CREB: A multifaceted transcriptional regulator of neural and immune function in CNS tumors.

Cancers of the central nervous system (CNS) are unique with respect to their tumor microenvironment. Such a status is due to immune-privilege and the cellular behaviors within a highly networked, neural-rich milieu. During tumor development in the CNS, neural, immune and cancer cells establish complex cell-to-cell communication networks which mimic physiological functions, including paracrine signaling and synapse-like formations. This crosstalk regulates diverse pathological functions contributing to tumor progression. In the CNS, regulation of physiological and pathological functions relies on various cell signaling and transcription programs. At the core of these events lies the cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), a master transcriptional regulator in the CNS. CREB is a kinase inducible transcription factor which regulates many CNS functions, including neurogenesis, neuronal survival, neuronal activation and long-term memory. Here, we discuss how CREB-regulated mechanisms operating in diverse cell types, which control development and function of the CNS, are co-opted in CNS tumors.

Technological advances define shifting pathway signaling from normal to primary and metastatic colorectal cancer.

Adoption of organoid/tumoroid propagation of normal and malignant intestinal epithelia has provided unparalleled opportunities to compare cell growth factor and signaling dependencies. These 3D structures recapitulate tumours in terms of gene expression regarding the tumor cells but also allow deeper insights into the contribution of the tumour microenvironment (TME). Elements of the TME can be manipulated or added back in the form of infiltrating cytotoxic lymphocytes and/or cancer associated fibroblasts. The effectiveness of chemo-, radio- and immunotherapies can be explored within weeks of deriving these patient-derived tumour avatars informing treatment of these exact patients in a timely manner. Entrenched paths to colorectal cancer (CRC) from the earliest steps of conventional adenoma or serrated lesion formation, and the recognition of further sub-categorisations embodied by consensus-molecular-subtypes (CMS), provide genetic maps allowing a molecular form of pathologic taxonomy. Recent advances in organoid propagation and scRNAseq are reshaping our understanding of CMS and CRC.

New insights into the unique nature of colorectal cancer peritoneal metastases-rethinking HIPEC.

Colorectal peritoneal metastases (CRPM) can be resistant to the chemotherapy agent (oxaliplatin) most employed, up until recently, as hyperthermic intraperitoneal chemotherapy (HIPEC). Glutathione-mediated inactivation of oxaliplatin can be substantially reduced by genomic deletion of the gene or pharmacological inhibition of glutamate-cysteine ligase in CRPM tumouroids. These discoveries may rekindle the enthusiasm for HIPEC in concert with cytoreductive surgery, which has been employed to manage patients with this once-nihilistic form of stage-IV disease.

Effect of Surgical Humidification on Inflammation and Peritoneal Trauma in Colorectal Cancer Surgery: A Randomized Controlled Trial.

BACKGROUND: Pre-clinical studies indicate that dry-cold-carbon-dioxide (DC-CO2) insufflation leads to more peritoneal damage, inflammation and hypothermia compared with humidified-warm-CO2 (HW-CO2). Peritoneum and core temperature in patients undergoing colorectal cancer (CRC) surgery were compared. METHODS: Sixty-six patients were randomized into laparoscopic groups; those insufflated with DC-CO2 or HW-CO2. A separate group of nineteen patients undergoing laparotomy were randomised to conventional surgery or with the insertion of a device delivering HW-CO2. Temperatures were monitored and peritoneal biopsies and bloods were taken at the start of surgery, at 1 and 3 h. Further bloods were taken depending upon hospital length-of-stay (LOS). Peritoneal samples were subjected to scanning electron microscopy to evaluate mesothelial damage. RESULTS: Laparoscopic cases experienced a temperature drop despite Bair-HuggerTM use. HW-CO2 restored normothermia (≥ 36.5 °C) by 3 h, DC-CO2 did not. LOS was shorter for colon compared with rectal cancer cases and if insufflated with HW-CO2 compared with DC-CO2; 5.0 vs 7.2 days, colon and 11.6 vs 15.4 days rectum, respectively. Unexpectedly, one third of patients had pre-existing damage. Damage increased at 1 and 3 h to a greater extent in the DC-CO2 compared with the HW-CO2 laparoscopic cohort. C-reactive protein levels were higher in open than laparoscopic cases and lower in both matched HW-CO2 groups. CONCLUSIONS: This prospective RCT is in accord with animal studies while highlighting pre-existing damage in some patients. Peritoneal mesothelium protection, reduced inflammation and restoration of core-body temperature data suggest benefit with the use of HW-CO2 in patients undergoing CRC surgery.

Synchronous Liver Resection, Cytoreductive Surgery, and Hyperthermic Intraperitoneal Chemotherapy for Colorectal Liver and Peritoneal Metastases: A Systematic Review and Meta-analysis.

BACKGROUND: Synchronous liver resection, cytoreductive surgery, and hyperthermic intraperitoneal chemotherapy for colorectal liver and peritoneal metastases have traditionally been contraindicated. More recent clinical practice has begun to promote this aggressive treatment in select patients. OBJECTIVE: This study aimed to investigate the perioperative and oncological outcomes of patients undergoing cytoreductive surgery and hyperthermic intraperitoneal chemotherapy, with and without liver resection, in the management of metastatic colorectal cancer. DATA SOURCES: Medline, Embase, and Cochrane Library databases were searched up to July 2020. STUDY SELECTION: Cohort studies comparing outcomes following cytoreductive surgery and hyperthermic intraperitoneal chemotherapy with and without liver resection for metastatic colorectal cancer were reviewed. No randomized controlled trials were available. INTERVENTION: Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy with or without synchronous liver resection were compared. MAIN OUTCOME MEASURES: The primary outcome measures were perioperative mortality and major morbidity. Secondary outcomes included 3- and 5-year overall survival and 1- and 3-year disease-free survival. RESULTS: Fourteen studies fitted the inclusion criteria, with 8 studies included in the meta-analysis. On pooled analysis, there was no significant difference in perioperative morbidity and mortality between the two groups. Patients that underwent concomitant liver resection had worse 1- and 3-year disease-free survival and 3- and 5-year overall survival. LIMITATIONS: Only a limited number of studies were available, with a moderate degree of heterogeneity. CONCLUSIONS: The addition of synchronous liver resection to cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for the treatment of resectable metastatic colorectal cancer was not associated with increased perioperative major morbidity and mortality in comparison with cytoreduction and hyperthermic intraperitoneal chemotherapy alone. However, the presence of liver metastases was associated with inferior disease-free and overall survival. These data support the continued practice of liver resection, cytoreductive surgery, and hyperthermic intraperitoneal chemotherapy in the management of select patients with such stage IV disease.

BET inhibitor resistance emerges from leukaemia stem cells.

Bromodomain and extra terminal protein (BET) inhibitors are first-in-class targeted therapies that deliver a new therapeutic opportunity by directly targeting bromodomain proteins that bind acetylated chromatin marks. Early clinical trials have shown promise, especially in acute myeloid leukaemia, and therefore the evaluation of resistance mechanisms is crucial to optimize the clinical efficacy of these drugs. Here we use primary mouse haematopoietic stem and progenitor cells immortalized with the fusion protein MLL-AF9 to generate several single-cell clones that demonstrate resistance, in vitro and in vivo, to the prototypical BET inhibitor, I-BET. Resistance to I-BET confers cross-resistance to chemically distinct BET inhibitors such as JQ1, as well as resistance to genetic knockdown of BET proteins. Resistance is not mediated through increased drug efflux or metabolism, but is shown to emerge from leukaemia stem cells both ex vivo and in vivo. Chromatin-bound BRD4 is globally reduced in resistant cells, whereas the expression of key target genes such as Myc remains unaltered, highlighting the existence of alternative mechanisms to regulate transcription. We demonstrate that resistance to BET inhibitors, in human and mouse leukaemia cells, is in part a consequence of increased Wnt/ß-catenin signalling, and negative regulation of this pathway results in restoration of sensitivity to I-BET in vitro and in vivo. Together, these findings provide new insights into the biology of acute myeloid leukaemia, highlight potential therapeutic limitations of BET inhibitors, and identify strategies that may enhance the clinical utility of these unique targeted therapies.

Prognostic Impact of Tumor-Infiltrating Lymphocytes in Primary and Metastatic Colorectal Cancer: A Systematic Review and Meta-analysis.

BACKGROUND: There is increasing literature emerging on the significance of tumor-infiltrating lymphocytes in colorectal cancer. However, there have been inconsistent findings, secondary to small patient numbers and varied methods for identifying these lymphocytes. OBJECTIVE: The aim of this study was to determine the prognostic and predictive power of tumor-infiltrating lymphocytes in colon, rectal (in neoadjuvant setting), and metastatic colorectal cancer. DATA SOURCES: A comprehensive search of PubMed and Embase was undertaken from January 2006 to December 2016. STUDY SELECTION: The inclusion criteria included a description of the tumor-infiltrating lymphocyte subset(s) assessed with reporting of associated short- and long-term outcomes. MAIN OUTCOME MEASURES: The main outcome measures, were disease-free and overall survival. RESULTS: A total of 25 studies were included, 15 for primary colorectal cancer (4719 patients), 7 for locally advanced rectal cancer (727 patients), and 3 studies for metastatic colorectal cancer (418 patients). High CD3, CD8, FoxP3, and CD45RO densities were associated with improved overall survival for primary colorectal cancer, with pooled estimated HRs of 0.88, 0.81, 0.70, and 0.63 (all p < 0.001) respectively. Furthermore, in locally advanced rectal cancer, the levels of CD8 cells were a significant predictor of good tumor regression grade after chemoradiotherapy. LIMITATIONS: The retrospective nature of included studies and the significant interstudy heterogeneity were limitations. CONCLUSIONS: There is increasing evidence that tumor-infiltrating lymphocytes play an important role in predicting prognosis in colorectal cancer and tumor regression after neoadjuvant chemoradiotherapy in locally advanced rectal cancer. Clinical researchers are now in a unique position to build on this work to identify robust predictive markers to stratify patients not only to currently available therapies but also to immunotherapy, which has demonstrated success in improving patient outcomes.

Risk Factors Associated With Circumferential Resection Margin Positivity in Rectal Cancer: A Binational Registry Study.

BACKGROUND: Rectal cancer outcomes have improved with the adoption of a multidisciplinary model of care. However, there is a spectrum of quality when viewed from a national perspective, as highlighted by the Consortium for Optimizing the Treatment of Rectal Cancer data on rectal cancer care in the United States. OBJECTIVE: The aim of this study was to assess and identify predictors of circumferential resection margin involvement for rectal cancer across Australasia. DESIGN: A retrospective study from a prospectively maintained binational colorectal cancer database was interrogated. SETTINGS: This study is based on a binational colorectal cancer audit database. PATIENTS: Clinical information on all consecutive resected rectal cancer cases recorded in the registry from 2007 to 2016 was retrieved, collated, and analyzed. MAIN OUTCOME MEASURES: The primary outcome measure was positive circumferential resection margin, measured as a resection margin ≤1 mm. RESULTS: A total of 3367 patients were included, with 261 (7.5%) having a positive circumferential resection margin. After adjusting for hospital and surgeon volume, hierarchical logistic regression analysis identified a 6-variable model encompassing the independent predictors, including urgent operation, abdominoperineal resection, open technique, low rectal cancer, T3 to T4, and N1 to N2. The accuracy of the model was 92.3%, with an receiver operating characteristic of 0.783 (p < 0.0001). The quantitative risk associated with circumferential resection margin positivity ranged from <1% (no risk factors) to 43% (6 risk factors). LIMITATIONS: This study was limited by the lack of recorded long-term outcomes associated with circumferential resection margin positivity. CONCLUSIONS: The rate of circumferential resection margin involvement in patients undergoing rectal cancer resection in Australasia is low and is influenced by a number of factors. Risk stratification of outcome is important with the increasing demand for publicly accessible quality data. See Video Abstract at http://links.lww.com/DCR/A512.

Salvage Surgery for Locoregional Failure in Anal Squamous Cell Carcinoma.

BACKGROUND: Anal squamous cell carcinoma is a rare cancer with a high cure rate, making research into the treatment of locoregional failure difficult. OBJECTIVE: The purpose of this study was to examine factors related to local treatment failure and determine the outcomes of patients undergoing local salvage resection. DESIGN: This was a retrospective cohort study. SETTING: This study was conducted at a quaternary referral center. PATIENTS: Patients with anal squamous cell carcinoma treated with chemoradiotherapy between January 1983 and December 2015 were included. MAIN OUTCOME MEASURES: The influence of patient-, tumor-, and treatment-related factors on the primary outcome measures of locoregional failure, overall survival, and disease-free survival were investigated. RESULTS: Of 467 patients with anal squamous cell carcinoma, 63 experienced locoregional failure with 41 undergoing salvage resection. Twenty-seven patients (38%) had persistent disease and 36 (62%) developed locoregional recurrence. Multivariate analysis identified tumor stage (HR, 3.16; p < 0.002) as an independent predictor of locoregional failure. Thirty abdominoperineal resections and 11 pelvic exenterations were undertaken with no surgical mortality. At a median follow-up of 20 months (range, 4-150 months), 5-year overall and disease-free survival for the salvage cohort was 51% and 47%. Margin positivity was an independent predictor for relapse post-salvage surgery on multivariate analysis (HR, 20.1; p = 0.027). Nineteen patients (48%) developed further relapse, which included all 10 patients with a positive resection margin, 3 of whom underwent re-resection. Of the 19 patients with relapse, 3 remain alive and 2 have persistent disease. LIMITATIONS: Limitations include the retrospective nature of the database, the prolonged time period of the study, and episodes of incomplete data. CONCLUSIONS: Advanced T stage is an independent predictor of local failure in anal squamous cell carcinoma. Most patients can be salvaged, with a positive resection margin being a strong predictor of further relapse and poor outcome. See Video Abstract at http://links.lww.com/DCR/A515.

Intratumor MAPK and PI3K signaling pathway heterogeneity in glioblastoma tissue correlates with CREB signaling and distinct target gene signatures.

Limitations in discovering useful tumor biomarkers and drug targets is not only due to patient-to-patient differences but also due to intratumor heterogeneity. Heterogeneity arises due to the genetic and epigenetic variation of tumor cells in response to microenvironmental interactions and cytotoxic therapy. We explored specific signaling pathway activation in glioblastoma (GBM) by investigating the intratumor activation of the MAPK and PI3K pathways. We present data demonstrating a striking preponderance for mutual exclusivity of MAPK and PI3K activation in GBM tissue, where MAPK activation correlates with proliferation and transcription factor CREB activation and PI3K activation correlates with CD44 expression. Bioinformatic analysis of signaling and CREB-regulated target genes supports the immunohistochemical data, showing that the MAPK-CREB activation correlates with proliferative regions. In-silico analysis suggests that MAPK-CREB signaling activates a pro-inflammatory molecular signature and correlates with a mesenchymal GBM subtype profile, while PI3K-CREB activation correlates with the proneural GBM subtype and a tumor cell invasive gene signature. Overall, the data suggests the existence of intratumor subtype heterogeneity in GBM and that using combinations of both MAPK and PI3K drug inhibitors is necessary for effective targeted therapy.

Outcome and Salvage Surgery Following "Watch and Wait" for Rectal Cancer after Neoadjuvant Therapy: A Systematic Review.

BACKGROUND: Currently there is no reliable test to predict pathological complete response following neoadjuvant chemoradiotherapy for rectal cancer. However, there is increasing interest in using clinical complete response as a surrogate marker, allowing a subset of patients with locally advanced rectal cancer to be allocated into a "watch and wait" pathway. Little is known about the oncological safety of the "watch and wait" approach or the rate of salvage surgery in cases of tumor regrowth. This information is critical for the implementation of this approach. OBJECTIVE: The aim of this study is to assess the rate of salvage surgery and associated oncological outcomes for patients who develop a tumor regrowth with the "watch and wait" approach. DATA SOURCES: Relevant studies were identified through PubMed, Embase, and Google Scholar search. STUDY SELECTION: A systematic review was undertaken of studies assessing patients selected for the "watch and wait" approach according to PRISMA guidelines. MAIN OUTCOME MEASURES: The associated tumor regrowth, salvage surgery, and disease-free and overall survival rates were assessed. RESULTS: Five retrospective and 4 prospective observational studies were included into the analysis, with a total of 370 patients in the "watch and wait" group, of which 256 (69.2%) had persistent clinical complete response. Of those who had tumor regrowth, salvage surgery was possible in 83.8%. There was no difference in overall survival and disease-free survival between patients who received immediate surgery and the "watch and wait" group. LIMITATIONS: The limitations of this study include its retrospective nature and small sample size. Furthermore, there is significant heterogeneity between study protocols, including the short median follow-up, given that tumor regrowth and distant metastasis may manifest at a later time point. CONCLUSION: The majority of patients with tumor regrowth can be salvaged with definite surgery after "watch and wait." However, there is insufficient evidence to draw firm conclusions on the oncological safety of this approach; therefore, it is currently not the standard of care for locally advanced rectal cancer.

Molecular biology of anal squamous cell carcinoma: implications for future research and clinical intervention.

Anal squamous cell carcinoma is a human papillomavirus-related disease, in which no substantial advances in treatment have been made in over 40 years, especially for those patients who develop disease relapse and for whom no surgical options exist. HPV can evade the immune system and its role in disease progression can be exploited in novel immunotherapy platforms. Although several studies have investigated the expression and inactivation (through loss of heterozygosity) of tumour suppressor genes in the pathways to cancer, no clinically valuable biomarkers have emerged. Regulators of apoptosis, including survivin, and agents targeting the PI3K/AKT pathway, offer opportunities for targeted therapy, although robust data are scarce. Additionally, antibody therapy targeting EGFR may prove effective, although its safety profile in combination with standard chemoradiotherapy has proven to be suboptimal. Finally, progress in the treatment of anal cancer has remained stagnant due to a lack of preclinical models, including cell lines and mouse models. In this Review, we discuss the molecular biology of anal squamous cell carcinoma, clinical trials in progress, and implications for novel therapeutic targets. Future work should focus on preclinical models to provide a resource for investigation of new molecular pathways and for testing novel targets.

Marker genes identify three somatic cell types in the fetal mouse ovary.

The two main functions of the ovary are the production of oocytes, which allows the continuation of the species, and secretion of female sex hormones, which control many aspects of female development and physiology. Normal development of the ovaries during embryogenesis is critical for their function and the health of the individual in later life. Although the adult ovary has been investigated in great detail, we are only starting to understand the cellular and molecular biology of early ovarian development. Here we show that the adult stem cell marker Lgr5 is expressed in the cortical region of the fetal ovary and this expression is mutually exclusive to FOXL2. Strikingly, a third somatic cell population can be identified, marked by the expression of NR2F2, which is expressed in LGR5- and FOXL2 double-negative ovarian somatic cells. Together, these three marker genes label distinct ovarian somatic cell types. Using lineage tracing in mice, we show that Lgr5-positive cells give rise to adult cortical granulosa cells, which form the follicles of the definitive reserve. Moreover, LGR5 is required for correct timing of germ cell differentiation as evidenced by a delay of entry into meiosis in Lgr5 loss-of-function mutants, demonstrating a key role for LGR5 in the differentiation of pre-granulosa cells, which ensure the differentiation of oogonia, the formation of the definitive follicle reserve, and long-term female fertility.

Myb via TGFß is required for collagen type 1 production and skin integrity.

Skin integrity requires an ongoing replacement and repair orchestrated by several cell types. We previously investigated the architecture of the skin of avian myeloblastosis viral oncogene homolog (Myb) knock-out (KO) embryos and wound repair in Myb(+/)(-) mice revealing a need for Myb in the skin, attributed to fibroblast-dependent production of collagen type 1. Here, using targeted Myb deletion in keratin-14 (K14) positive cells we reveal further Myb-specific defects in epidermal cell proliferation, thickness and ultrastructural morphology. This was associated with a severe deficit in collagen type 1 production, reminiscent of that observed in patients with ichthyosis vulgaris and Ehlers-Danlos syndrome. Since collagen type 1 is a product of fibroblasts, the collagen defect observed was unexpected and appears to be directed by the loss of Myb with significantly reduced tumor growth factor beta 1 (Tgfß-1) expression by primary keratinocytes. Our findings support a specific role for Myb in K14+ epithelial cells in the preservation of adult skin integrity and function.

RAD21 mutations cause a human cohesinopathy.

The evolutionarily conserved cohesin complex was originally described for its role in regulating sister-chromatid cohesion during mitosis and meiosis. Cohesin and its regulatory proteins have been implicated in several human developmental disorders, including Cornelia de Lange (CdLS) and Roberts syndromes. Here we show that human mutations in the integral cohesin structural protein RAD21 result in a congenital phenotype consistent with a "cohesinopathy." Children with RAD21 mutations display growth retardation, minor skeletal anomalies, and facial features that overlap findings in individuals with CdLS. Notably, unlike children with mutations in NIPBL, SMC1A, or SMC3, these individuals have much milder cognitive impairment than those with classical CdLS. Mechanistically, these mutations act at the RAD21 interface with the other cohesin proteins STAG2 and SMC1A, impair cellular DNA damage response, and disrupt transcription in a zebrafish model. Our data suggest that, compared to loss-of-function mutations, dominant missense mutations result in more severe functional defects and cause worse structural and cognitive clinical findings. These results underscore the essential role of RAD21 in eukaryotes and emphasize the need for further understanding of the role of cohesin in human development.

Cohesin regulates tissue-specific expression by stabilizing highly occupied cis-regulatory modules.

The cohesin protein complex contributes to transcriptional regulation in a CTCF-independent manner by colocalizing with master regulators at tissue-specific loci. The regulation of transcription involves the concerted action of multiple transcription factors (TFs) and cohesin's role in this context of combinatorial TF binding remains unexplored. To investigate cohesin-non-CTCF (CNC) binding events in vivo we mapped cohesin and CTCF, as well as a collection of tissue-specific and ubiquitous transcriptional regulators using ChIP-seq in primary mouse liver. We observe a positive correlation between the number of distinct TFs bound and the presence of CNC sites. In contrast to regions of the genome where cohesin and CTCF colocalize, CNC sites coincide with the binding of master regulators and enhancer-markers and are significantly associated with liver-specific expressed genes. We also show that cohesin presence partially explains the commonly observed discrepancy between TF motif score and ChIP signal. Evidence from these statistical analyses in wild-type cells, and comparisons to maps of TF binding in Rad21-cohesin haploinsufficient mouse liver, suggests that cohesin helps to stabilize large protein-DNA complexes. Finally, we observe that the presence of mirrored CTCF binding events at promoters and their nearby cohesin-bound enhancers is associated with elevated expression levels.

Peritoneal Tumorigenesis and Inflammation are Ameliorated by Humidified-Warm Carbon Dioxide Insufflation in the Mouse.

BACKGROUND: Conventional laparoscopic surgery uses CO2 that is dry and cold, which can damage peritoneal surfaces. It is speculated that disseminated cancer cells may adhere to such damaged peritoneum and metastasize. We hypothesized that insufflation using humidified-warm CO2, which has been shown to reduce mesothelial damage, will also ameliorate peritoneal inflammation and tumor cell implantation compared to conventional dry-cold CO2. METHODS: Laparoscopic insufflation was modeled in mice along with anesthesia and ventilation. Entry and exit ports were introduced to maintain insufflation using dry-cold or humidified-warm CO2 with a constant flow and pressure for 1 h; then 1000 or 1 million fluorescent-tagged murine colorectal cancer cells (CT26) were delivered into the peritoneal cavity. The peritoneum was collected at intervals up to 10 days after the procedure to measure inflammation, mesothelial damage, and tumor burden using fluorescent detection, immunohistochemistry, and scanning electron microscopy. RESULTS: Rapid temperature control was achieved only in the humidified-warm group. Port-site tumors were present in all mice. At 10 days, significantly fewer tumors on the peritoneum were counted in mice insufflated with humidified-warm compared to dry-cold CO2 (p < 0.03). The inflammatory marker COX-2 was significantly increased in the dry-cold compared to the humidified-warm cohort (p < 0.01), while VEGFA expression was suppressed only in the humidified-warm cohort. Significantly less mesothelial damage and tumor cell implantation was evident from 2 h after the procedure in the humidified-warm cohort. CONCLUSIONS: Mesothelial cell damage and inflammation are reduced by using humidified-warm CO2 for laparoscopic oncologic surgery and may translate to reduce patients' risk of developing peritoneal metastasis.

Physiological expression of the PI3K-activating mutation Pik3ca(H1047R) combines with Apc loss to promote development of invasive intestinal adenocarcinomas in mice.

PIK3CA, the gene encoding the p110α catalytic subunit of PI3K (phosphoinositide 3-kinase), is mutated in approximately 20% of sporadic CRCs (colorectal cancers), but the role of these mutations in the pathogenesis of CRC remains unclear. In the present study we used a novel mouse model to investigate the role of the Pik3caH1047R mutation, the most common PIK3CA mutation in CRC, during the development and progression of intestinal cancer. Our results demonstrate that Pik3caH1047R, when expressed at physiological levels, is insufficient to initiate intestinal tumorigenesis; however, in the context of Apc (adenomatous polyposis coli) loss, which is observed in 80% of CRCs and by itself results in benign intestinal adenomas, the Pik3caH1047R mutation promotes the development of highly aggressive and invasive adenocarcinomas in both the small and large intestines. The results of the present study show that an activating Pik3ca mutation can act in tandem with Apc loss to drive the progression of gastrointestinal cancer and thus this disease may be susceptible to therapeutic targeting using PI3K pathway inhibitors.

Estrogen receptor-α recruits P-TEFb to overcome transcriptional pausing in intron 1 of the MYB gene.

The MYB proto-oncogene is expressed in most estrogen receptor-positive (ERα(+)) breast tumors and cell lines. Expression of MYB is controlled, in breast cancer and other cell types, by a transcriptional pausing mechanism involving an attenuation site located ∼1.7 kb downstream from the transcription start site. In breast cancer cells, ligand-bound ERα binds close to, and drives transcription beyond this attenuation site, allowing synthesis of complete transcripts. However, little is known, in general, about the factors involved in relieving transcriptional attenuation, or specifically how ERα coordinates such factors to promote transcriptional elongation. Using cyclin dependent kinase 9 (CDK9) inhibitors, reporter gene assays and measurements of total and intronic MYB transcription, we show that functionally active CDK9 is required for estrogen-dependent transcriptional elongation. We further show by ChIP and co-immunoprecipitation studies that the P-TEFb complex (CDK9/CyclinT1) is recruited to the attenuation region by ligand-bound ERα, resulting in increased RNA polymerase II Ser-2 phosphorylation. These data provide new insights into MYB regulation, and given the critical roles of MYB in tumorigenesis, suggest targeting MYB elongation as potential therapeutic strategy.