Interplay between pleiotropy and secondary selection determines rise and fall of mutators in stress response

Dramatic rise of mutators has been found to accompany adaptation of bacteria in response to many kinds of stress. Two views on the evolutionary origin of this phenomenon emerged: the pleiotropic hypothesis positing that it is a byproduct of environmental stress or other specific stress response mechanisms and the second order selection which states that mutators hitchhike to fixation with unrelated beneficial alleles. Conventional population genetics models could not fully resolve this controversy because they are based on certain assumptions about fitness landscape. Here we address this problem using a microscopic multiscale model, which couples physically realistic molecular descriptions of proteins and their interactions with population genetics of carrier organisms without assuming any a priori fitness landscape. We found that both pleiotropy and second order selection play a crucial role at different stages of adaptation: the supply of mutators is provided through destabilization of error correction complexes or fluctuations of production levels of prototypic mismatch repair proteins (pleiotropic effects), while rise and fixation of mutators occur when there is a sufficient supply of beneficial mutations in replication-controlling genes. This general mechanism assures a robust and reliable adaptation of organisms to unforeseen challenges. This study highlights physical principles underlying physical biological mechanisms of stress response and adaptation

The stress-responsive kinase DYRK2 activates heat shock factor 1 promoting resistance to proteotoxic stress

To survive proteotoxic stress, cancer cells activate the proteotoxic-stress response pathway, which is controlled by the transcription factor heat shock factor 1 (HSF1). This pathway supports cancer initiation, cancer progression and chemoresistance and thus is an attractive therapeutic target. As developing inhibitors against transcriptional regulators, such as HSF1 is challenging, the identification and targeting of upstream regulators of HSF1 present a tractable alternative strategy. Here we demonstrate that in triple-negative breast cancer (TNBC) cells, the dual specificity tyrosine-regulated kinase 2 (DYRK2) phosphorylates HSF1, promoting its nuclear stability and transcriptional activity. DYRK2 depletion reduces HSF1 activity and sensitises TNBC cells to proteotoxic stress. Importantly, in tumours from TNBC patients, DYRK2 levels positively correlate with active HSF1 and associates with poor prognosis, suggesting that DYRK2 could be promoting TNBC. These findings identify DYRK2 as a key modulator of the HSF1 transcriptional programme and a potential therapeutic target

Mutant p53 as a guardian of the cancer cell

Forty years of research have established that the p53 tumor suppressor provides a major barrier to neoplastic transformation and tumor progression by its unique ability to act as an extremely sensitive collector of stress inputs, and to coordinate a complex framework of diverse effector pathways and processes that protect cellular homeostasis and genome stability. Missense mutations in the TP53 gene are extremely widespread in human cancers and give rise to mutant p53 proteins that lose tumor suppressive activities, and some of which exert trans-dominant repression over the wild-type counterpart. Cancer cells acquire selective advantages by retaining mutant forms of the protein, which radically subvert the nature of the p53 pathway by promoting invasion, metastasis and chemoresistance. In this review, we consider available evidence suggesting that mutant p53 proteins can favor cancer cell survival and tumor progression by acting as homeostatic factors that sense and protect cancer cells from transformation-related stress stimuli, including DNA lesions, oxidative and proteotoxic stress, metabolic inbalance, interaction with the tumor microenvironment, and the immune system. These activities of mutant p53 may explain cancer cell addiction to this particular oncogene, and their study may disclose tumor vulnerabilities and synthetic lethalities that could be exploited for hitting tumors bearing missense TP53 mutations

Fibronectin is a stress responsive gene regulated by HSF1 in response to geldanamycin

Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended

P3-01-09: Oncogenic Activation of HSF1 Enables the Malignant Progression of Breast Carcinoma.

Abstract HSF1 is best known for its role as the master transcriptional regulator of the evolutionarily conserved heat-shock response. In mice, Hsf1 knock-outs dramatically reduce susceptibility to malignant transformation and tumor formation, and markedly increased survival in cancers driven by both oncogenic and tumor suppressor mutations. Likewise, RNAi-mediated knockdown markedly reduces the growth and survival of human cell lines established from cancers driven by a diversity of genetic lesions. The transcriptional network that HSF1 coordinates during heat-shock is known, but is unknown in malignancy. We compare HSF1 function in isogenic breast cancer cells of high and low malignant potential. HSF1 orchestrates a far-reaching transcriptional program that is dependent on transformation and the degree of malignancy. The oncogenic HSF1 program differs markedly from the classical heat-shock response. It is enriched for genes involved in a myriad of cellular processes known to be important in malignancy, including transcription, translation, glucose metabolism and cellular adhesion. It includes only a particular subset of heat-shock protein genes, and many of these are regulated in a manner that differs from their regulation by heat-shock. We also find that HSF1 is overexpressed and activated in a large subset of all conventionally defined classes of breast cancer. Moreover, tumors with high expression of the oncogenic HSF1 transcriptional network are strongly associated with poor outcome as monitored by metastasis and death. Our findings suggest that the oncogenic HSF1 activation program is rooted in fundamental aspects of tumor biology and will prove a powerful new tool in the clinical management of patients with breast cancer and, likely, other malignancies as well. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-01-09.</jats:p

P5-01-13: High Levels of Nuclear Heat Shock Factor 1 (HSF1) Are Associated with Poor Prognosis in Breast Cancer: Results from the Nurses' Health Study.

Abstract Purpose: Heat shock factor 1 (HSF1) is the master transcriptional regulator of the cellular response to heat and a wide variety of other stressors. We previously reported that HSF1 promotes the survival and proliferation of malignant cells. At this time, however, the clinical and prognostic significance of HSF1 in cancer is unknown. Patients and methods: Breast cancer samples from 1,841 participants in the Nurses’ Health Study (NHS) were scored for levels of nuclear HSF1. Associations of HSF1 status with clinical parameters and survival outcomes were investigated by Kaplan-Meier analysis and Cox proportional hazard models. The associations were further delineated by Kaplan-Meier analysis using publicly available mRNA expression data. Results: Nuclear HSF1 levels were elevated in ∼80% of in situ and invasive breast carcinomas. In invasive carcinomas, HSF1 expression was associated with high histologic grade, larger tumor size, and nodal involvement at diagnosis (P&amp;lt;0.0001). Overall, in multivariate analysis, high-HSF1 levels were associated with increased breast cancer-specific mortality (HR, 1.62; 95% CI, 1.21−2.17). This association was seen in the ER-positive population (HR, 2.10; 95% CI, 1.25−2.47), even in early-stage lymph node negative cases (HR, 1.98; 95% CI, 1.17−3.33). In public expression profiling data, high-HSF1 mRNA levels were also associated with an increase in ER-positive breast cancer-specific mortality. Conclusions: Increased HSF1 is associated with reduced survival in breast cancer. The findings indicate that HSF1 should be evaluated prospectively as an independent prognostic indicator in ER-positive breast cancer and that HSF1 may provide a useful therapeutic target. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-01-13.</jats:p

Conformational changes in the G protein Gs induced by the β2 adrenergic receptor

G protein-coupled receptors (GPCRs) represent the largest family of membrane receptors(1) that instigate signaling through nucleotide exchange on heterotrimeric G proteins. Nucleotide exchange, or more precisely GDP dissociation from the G protein α-subunit, is the key step toward G protein activation and initiation of downstream signaling cascades. Despite a wealth of biochemical and biophysical studies on inactive and active conformations of several heterotrimeric G proteins, the molecular underpinnings of G protein activation remain elusive. To characterize this mechanism we applied peptide amide hydrogen-deuterium exchange mass spectrometry (DXMS) to probe changes in the structure of the heterotrimeric G protein Gs (the stimulatory G protein for adenylyl cyclase) upon formation of a complex with agonist-bound β(2) adrenergic receptor (β(2)AR). Our studies reveal structural links between the receptor binding surface and the nucleotide-binding pocket of Gs that undergo higher levels of hydrogen-deuterium exchange (HX) than would be predicted from the crystal structure of the β(2)AR-Gs complex. Together with x-ray crystallographic and electron microscopic data of the β(2)AR-Gs complex (ref 2 and Westfield et al, manuscript submitted), we provide a rationale for a mechanism of nucleotide exchange whereby the receptor perturbs the structure of the amino-terminal region of α-subunit of Gs and consequently alters the ‘P-loop’ that binds the β-phosphate in GDP. As with the ras-family of small molecular weight G proteins, P-loop stabilization and β-phosphate coordination are key determinants of GDP (and GTP) binding affinity