Does walking during chemotherapy impact p16INK4a levels in women with early breast cancer.

BACKGROUND: Increased p16INK4a (p16) expression is directly related to cellular senescence and is a robust biomarker of aging in humans. Prior studies have shown that levels of p16 dramatically increase in breast cancer patients who have received adjuvant chemotherapy. This study investigated whether moderate physical activity during chemotherapy would attenuate the expected rise in p16 expression. METHODS: Participants were women with Stage I-III breast cancer enrolled in a walking study for the duration of their chemotherapy (NCT02167932, NCT02328313, NCT03761706). Participants were asked to walk at least 30 min or 6200 steps/day following a structured walking program and to wear an activity tracker. p16 mRNA levels were measured in peripheral blood T-cells before chemotherapy initiation and at approximately 6 months after last chemotherapy treatment (mean 200 days, SD 40 days). RESULTS: In total, 141 participants met inclusion criteria and 10% (n = 14) averaged > 6200 steps/day. There was no significant association of daily steps with change in p16 levels pre- to post-chemotherapy (Pearson correlation coefficient = 0.11, p = 0.17). After adjusting for age, stage, anthracycline-based chemotherapy, and baseline p16, the change in log2 p16 for each 1000 steps was estimated to be 0.03 (p = 0.35). Most participants were sedentary prior to chemotherapy and achieved modest levels of physical activity during treatment. CONCLUSION: A self-guided walking program achieved only modest levels of physical activity and was unable to ameliorate chemotherapy-induced change in p16 levels in women undergoing chemotherapy for early-stage breast cancer. More structured and vigorous exercise programs should be tested for a more definitive exploration of their impact on post-chemotherapy p16 levels.

Accelerated aging among childhood, adolescent, and young adult cancer survivors is evidenced by increased expression of p16INK4a and frailty.

BACKGROUND: Cellular senescence, measured by expression of the cell cycle kinase inhibitor p16INK4a , may contribute to accelerated aging in survivors of childhood, adolescent, and young adult cancer. The authors measured peripheral blood T-lymphocyte p16INK4a expression among pediatric and young adult cancer survivors, hypothesizing that p16INK4a expression is higher after chemotherapy and among frail survivors. METHODS: A cross-sectional cohort of young adult survivors and age-matched, cancer-free controls were assessed for p16INK4a expression and frailty. Newly diagnosed pediatric patients underwent prospective measurements of p16INK4a expression before and after cancer therapy. Frailty was measured with a modified Fried frailty phenotype evaluating sarcopenia, weakness, slowness, energy expenditure, and exhaustion. RESULTS: The cross-sectional cohort enrolled 60 survivors and 29 age-matched controls with a median age of 21 years (range, 17-29 years). The prospective cohort enrolled 9 newly diagnosed patients (age range, 1-18 years). Expression of p16INK4a was higher among survivors compared with controls (9.6 vs 8.9 log2 p16 units; 2-sided P = .005, representing a 25-year age acceleration in survivors) and increased among newly diagnosed patients from matched pretreatment to posttreatment samples (7.3-8.9 log2 p16 units; 2-sided P = .002). Nine survivors (16%) were frail and had higher p16INK4a expression compared with robust survivors (10.5 [frail] vs 9.5 [robust] log2 p16 units; 2-sided P = .055), representing a 35-year age acceleration among frail survivors. CONCLUSIONS: Chemotherapy is associated with increased cellular senescence and molecular age in pediatric and young adult cancer survivors. Frail survivors, compared with robust survivors, exhibit higher levels of p16INK4a , suggesting that cellular senescence may be associated with early aging in survivors.

TEM4 is a junctional Rho GEF required for cell-cell adhesion, monolayer integrity and barrier function.

Signaling events mediated by Rho family GTPases orchestrate cytoskeletal dynamics and cell junction formation. The activation of Rho GTPases is tightly regulated by guanine-nucleotide-exchange factors (GEFs). In this study, we identified a novel Rho-specific GEF called TEM4 (tumor endothelial marker 4) that associates with multiple members of the cadherin-catenin complex and with several cytoskeleton-associated proteins. Depending on confluence, TEM4 localized to either actin stress fibers or areas of cell-cell contact. The junctional localization of TEM4 was independent of actin binding. Depletion of endogenous TEM4 by shRNAs impaired Madin-Darby canine kidney (MDCK) and human umbilical vein endothelial cell (HUVEC) cell junctions, disrupted MDCK acini formation in 3D culture and negatively affected endothelial barrier function. Taken together, our findings implicate TEM4 as a novel and crucial junctional Rho GEF that regulates cell junction integrity and epithelial and endothelial cell function.

Caloric Restriction Intervention Alters Specific Circulating Biomarkers of the Senescence-Associated Secretome in Middle-Aged and Older Adults With Obesity and Prediabetes in an 18-Week Randomized Controlled Trial.

Cellular senescence is a biological aging process that is exacerbated by obesity and leads to inflammation and age- and obesogenic-driven chronic diseases including type 2 diabetes. Caloric restriction (CR) may improve metabolic function in part by reducing cellular senescence and the pro-inflammatory senescence-associated phenotype (SASP). We conducted an ancillary investigation of an 18-week randomized controlled trial (RCT) of CR (n = 31) or Control (n = 27) in 58 middle-aged/older adults (57.6 ±â€…5.8 years; 75% Women) with obesity and prediabetes. We measured mRNA expression of select senescence and apoptosis genes in blood CD3 + T cells (qRT-PCR) and a panel of 25 plasma SASP proteins (Luminex/multiplex; ELISA). Participants randomized to CR lost -10.8 ±â€…0.9 kg (-11.3% ±â€…5.4%) over 18 weeks compared with +0.5 ±â€…0.9 kg (+0.03% ±â€…3.5%) in Control group. T-cell expression of senescence biomarkers, p16INK4a and p21CIP1/WAF1, and apoptosis markers, BCL2L1 and BAK1, was not different between CR and Control groups in age, race, and sex-adjusted mixed models (p > .05, all). Iterative principal axis factor analysis was used to develop composite SASP Factors, and the Factors comprising TNFRI, TNFRII, uPAR, MMP1, GDF15, OPN, Fas, and MPO were significantly altered with CR intervention (age, sex, race-adjusted mixed model time × treatment F = 4.17, p ≤ .05) and associated with the degree of weight loss (R2 = 0.12, p ≤ .05). Our study provides evidence from an RCT that specific circulating biomarkers of senescent cell burden are changed by CR in middle-aged and older adults with obesity and prediabetes. Future studies compare tissue and circulating levels of p16INK4a and pro-inflammatory SASP biomarkers in other populations, and interventions.

Phosphorylation by protein kinase Cα regulates RalB small GTPase protein activation, subcellular localization, and effector utilization.

Ras-like (Ral) small GTPases are regulated downstream of Ras and the noncanonical Ral guanine nucleotide exchange factor (RalGEF) effector pathway. Despite RalA and RalB sharing 82% sequence identity and utilization of shared effector proteins, their roles in normal and neoplastic cell growth have been shown to be highly distinct. Here, we determined that RalB function is regulated by protein kinase Cα (PKCα) phosphorylation. We found that RalB phosphorylation on Ser-198 in the C-terminal membrane targeting sequence resulted in enhanced RalB endomembrane accumulation and decreased RalB association with its effector, the exocyst component Sec5. Additionally, RalB phosphorylation regulated vesicular trafficking and membrane fusion by regulating v- and t-SNARE interactions. RalB phosphorylation regulated vesicular traffic of α5-integrin to the cell surface and cell attachment to fibronectin. In summary, our data suggest that phosphorylation by PKCα is critical for RalB-mediated vesicle trafficking and exocytosis.

A signature of pre-operative biomarkers of cellular senescence to predict risk of cardiac and kidney adverse events after cardiac surgery.

Objective: Understand the potential for pre-operative biomarkers of cellular senescence, a primary aging mechanism, to predict risk of cardiac surgery-associated adverse events. Methods: Biomarkers of senescence were assessed in blood samples collected prior to surgery in 331 patients undergoing CABG +/-valve repair or replacement. Patients were followed throughout the hospital stay and at a 30-day follow-up visit. Logistic regression models for pre-operative risk prediction were built for age-related clinical outcomes with high incidence including KDIGO-defined acute kidney injury (AKI), decline in eGFR ≥25% between pre-op and 30 days, and MACKE30, a composite endpoint of major adverse cardiac and kidney events at 30d. Results: AKI occurred in 19.9% of patients, persistent decline in kidney function at 30d occurred in 11.0%, and MACKE30 occurred in 13.4%. A network of six biomarkers of senescence (p16, p14, LAG3, CD244, CD28 and suPAR) were able to identify patients at risk for AKI (AUC 0.76), kidney decline at 30d (AUC 0.73), and MACKE30 (AUC 0.71). Comparing the top and bottom tertiles of senescence-based risk models, patients in the top tertile had 7.8 (3.3-8.4) higher odds of developing AKI, 4.5 (1.6-12.6) higher odds of developing renal decline at 30d, and 5.7 (2.1-15.6) higher odds of developing MACKE30. All models remained significant when adjusted for clinical variables. Patients with kidney function decline at 30d were largely non-overlapping and clinically distinct from those who experienced AKI, suggesting a different etiology. Typical clinical factors that predispose to AKI (e.g., age, CKD, surgery type) associated with AKI but not the 30d decline endpoint which was instead associated with new-onset atrial fibrillation. Conclusions: A six-member network of biomarkers of senescence, a fundamental mechanism of aging, can identify patients for risk of adverse kidney and cardiac events when measured pre-operatively.

Profiling an integrated network of cellular senescence and immune resilience measures in natural aging: a prospective multi-cohort study.

Background: Biological aging begins decades before the onset of age-related clinical conditions and is mediated by both cellular senescence and declining adaptive immune function. These processes are functionally related with the rate of senescent cell accumulation dependent upon a balance between induction and immune clearance. We previously showed that biomarkers in these domains can identify patients at-risk of surgery-related adverse events. Here, we describe evidence of clinical relevance in early aging and metabolic phenotypes in a general adult population. Methods: We enrolled a total of 482 participants (ages 25-90) into two prospective, cross-sectional healthy aging cohorts. Expression of biomarkers of adaptive immune function and cellular senescence (SapereX) was measured in CD3+ T cells isolated from peripheral blood. Findings: We established a network of biomarkers of adaptive immune function that correlate with cellular senescence and associate with early aging phenotypes. SapereX immune components associated with a decrease in CD4+ T cells, an increase in cytotoxic CD8+ T cells, and a loss of CD8+ naïve T cells (Pearson correlation 0.3-0.6). These components also associated with a metric of immune resilience, an ability to withstand antigen challenge and inflammation. In contrast, SapereX components were only weakly associated with GlycanAge (Pearson correlation 0.03-0.15) and commonly used DNA methylation clocks (Pearson correlation 0-0.25). Finally, SapereX biomarkers, in particular p16, were associated with chronic inflammation and metabolic dysregulation. Interpretation: Measurement of SapereX biomarkers may capture essential elements of the relationship between cellular senescence and dysregulated adaptive immune function and may provide a benchmark for clinically relevant health decisions.

Release of autoinhibition of ASEF by APC leads to CDC42 activation and tumor suppression.

Autoinhibition of the Rho guanine nucleotide exchange factor ASEF is relieved by interaction with the APC tumor suppressor. Here we show that binding of the armadillo repeats of APC to a 'core APC-binding' (CAB) motif within ASEF, or truncation of the SH3 domain of ASEF, relieves autoinhibition, allowing the specific activation of CDC42. Structural determination of autoinhibited ASEF reveals that the SH3 domain forms an extensive interface with the catalytic DH and PH domains to obstruct binding and activation of CDC42, and the CAB motif is positioned adjacent to the SH3 domain to facilitate activation by APC. In colorectal cancer cell lines, full-length, but not truncated, APC activates CDC42 in an ASEF-dependent manner to suppress anchorage-independent growth. We therefore propose a model in which ASEF acts as a tumor suppressor when activated by APC and inactivation of ASEF by mutation or APC truncation promotes tumorigenesis.

A biomarker of aging, p16, predicts peripheral neuropathy in women receiving adjuvant taxanes for breast cancer.

Identifying patients at higher risk of chemotherapy-induced peripheral neuropathy (CIPN) is a major unmet need given its high incidence, persistence, and detrimental effect on quality of life. We determined if the expression of p16, a biomarker of aging and cellular senescence, predicts CIPN in a prospective, multi-center study of 152 participants enrolled between 2014 and 2018. Any women with newly diagnosed Stage I-III breast cancer scheduled to receive taxane-containing chemotherapy was eligible. The primary outcome was development of grade 2 or higher CIPN during chemotherapy graded by the clinician before each chemotherapy cycle (NCI-CTCAE v5 criteria). We measured p16 expression in peripheral blood T cells by qPCR before and at the end of chemotherapy. A multivariate model identified risk factors for CIPN and included taxane regimen type, p16Age Gap, a measure of discordance between chronological age and p16 expression, and p16 expression before chemotherapy. Participants with higher p16Age Gap-higher chronological age but lower p16 expression prior to chemotherapy - were at the highest risk. In addition, higher levels of p16 before treatment, regardless of patient age, conferred an increased risk of CIPN. Incidence of CIPN positively correlated with chemotherapy-induced increase in p16 expression, with the largest increase seen in participants with the lowest p16 expression before treatment. We have shown that p16 expression levels before treatment can identify patients at high risk for taxane-induced CIPN. If confirmed, p16 might help guide chemotherapy selection in early breast cancer.

p16 a biomarker of aging and tolerance for cancer therapy.

There is great variability in life-expectancy, physical, cognitive, and functional domains in cancer patients of similar chronologic age. Nowhere is this more apparent than among middle-aged and older patients. However, even in younger patients of similar age, extensive exposure to environmental stressors can cause great variability in health status. A biomarker that would reflect biologic age and any and all health deficits in a cancer patient at a distinct point in time might help predict long term outcomes related to treatment, especially toxicity and overall survival. p16INK4a (hereafter referred to as p16) expression represents an ideal biomarker that reflects both cellular senescence and biologic aging. In murine models, p16 expression reflects biologic aging in almost all organs. Preliminary findings in patients with cancer support p16 measurement as a marker of physiologic aging and predictor of toxicity in patients treated with chemotherapy. This review describes the role of p16 in cell senescence, the methodology of p16 measurement in humans, preliminary studies of p16 in humans, and the potential clinical utility of p16 in guiding treatment for cancer patients.

Effects of Breast Cancer Adjuvant Chemotherapy Regimens on Expression of the Aging Biomarker, p16INK4a.

BACKGROUND: Although chemotherapy saves lives, increasing evidence shows that chemotherapy accelerates aging. We previously demonstrated that mRNA expression of p16INK4a , a biomarker of senescence and molecular aging, increased early and dramatically after beginning adjuvant anthracycline-based regimens in early stage breast cancer patients. Here, we determined if changes in p16INK4a expression vary by chemotherapy regimen among early stage breast cancer patients. METHODS: We conducted a study of stage I-III breast cancer patients receiving adjuvant or neoadjuvant chemotherapy. p16INK4a expression was analyzed prechemotherapy and postchemotherapy (median 6.2 months after the last chemotherapy) in peripheral blood T lymphocytes. Chemotherapy-induced change in p16INK4a expression was compared among regimens. All statistical tests were 2-sided. RESULTS: In 146 women, chemotherapy was associated with a statistically significant increase in p16INK4a expression (accelerated aging of 17 years; P < .001). Anthracycline-based regimens were associated with the largest increases (accelerated aging of 23 to 26 years; P ≤ .008). Nonanthracycline-based regimens demonstrated a much smaller increase (accelerated aging of 9 to 11 years; P ≤ .15). In addition to the type of chemotherapy regimen, baseline p16INK4a levels, but not chronologic age or race, were also associated with the magnitude of increases in p16INK4a . Patients with lower p16INK4a levels at baseline were more likely to experience larger increases. CONCLUSIONS: Our findings suggest that the aging effects of chemotherapy may be influenced by both chemotherapy type and the patient's baseline p16INK4a level. Measurement of p16INK4a expression is not currently available in the clinic, but nonanthracycline regimens offering similar efficacy as anthracycline regimens might be favored.

Multiple sequence elements facilitate Chp Rho GTPase subcellular location, membrane association, and transforming activity.

Cdc42 homologous protein (Chp) is a member of the Rho family of small GTPases and shares significant sequence and functional similarity with Cdc42. However, unlike classical Rho GTPases, we recently found that Chp depends on palmitoylation, rather than prenylation, for association with cellular membranes. Because palmitoylation alone is typically not sufficient to promote membrane association, we evaluated the possibility that other carboxy-terminal residues facilitate Chp subcellular association with membranes. We found that Chp membrane association and transforming activity was dependent on the integrity of a stretch of basic amino acids in the carboxy terminus of Chp and that the basic amino acids were not simply part of a palmitoyl acyltransferase recognition motif. We also determined that the 11 carboxy-terminal residues alone were sufficient to promote Chp plasma and endomembrane association. Interestingly, stimulation with tumor necrosis factor-alpha activated only endomembrane-associated Chp. Finally, we found that Chp membrane association was not disrupted by Rho guanine nucleotide dissociation inhibitory proteins, which are negative regulators of Cdc42 membrane association and biological activity. In summary, the unique carboxy-terminal sequence elements that promote Chp subcellular location and function expand the complexity of mechanisms by which the cellular functions of Rho GTPases are regulated.

Signaling interplay in Ras superfamily function.

Ras proteins function as signaling hubs that are activated by convergent signaling pathways initiated by extracellular stimuli. Activated Ras in turn regulates a diversity of downstream cytoplasmic signaling cascades. Ras proteins are founding members of a large superfamily of small GTPases that have significant sequence and biochemical similarities. Recent observations have established a complex signaling interplay between Ras and other members of the family. A key biochemical mechanism facilitating this crosstalk involves guanine nucleotide exchange factors (GEFs), which serve as regulators and effectors, as well as signaling integrators, of Ras signaling.

Mist1-KrasG12D knock-in mice develop mixed differentiation metastatic exocrine pancreatic carcinoma and hepatocellular carcinoma.

Despite the prevalence of oncogenic Kras mutations in the earliest stages of pancreatic ductal adenocarcinoma, the cellular compartment in which oncogenic Kras initiates tumorigenesis remains unknown. To address this, we have gene targeted KrasG12D into the open reading frame of Mist1, a basic helix-loop-helix transcription factor that is expressed during pancreatic development and required for proper pancreatic acinar organization. Although the pancreata of Mist1(KrasG12D/+) mutant mice predictably exhibited acinar metaplasia and dysplasia, the frequent death of these mice from invasive and metastatic pancreatic cancer with mixed histologic characteristics, including acinar, cystic, and ductal features, was unexpected and in contrast to previously described mutant mice that ectopically expressed the Kras oncogene in either acinar or ductal compartments. Interestingly, many of the mutant mice developed hepatocellular carcinoma, implicating Mist1(KrasG12D/+) cells in both pancreatic and hepatic neoplasia. Concomitant Trp53+/- mutation cooperated with Mist1(KrasG12D/+) to accelerate lethality and was associated with advanced histopathologic findings, including parenchymal liver metastasis. These findings suggest that Mist1-expressing cells represent a permissive compartment for transformation by oncogenic Kras in pancreatic tumorigenesis.

Expression of p16INK4a is a biomarker of chondrocyte aging but does not cause osteoarthritis.

Cellular senescence drives a functional decline of numerous tissues with aging by limiting regenerative proliferation and/or by producing pro-inflammatory molecules known as the senescence-associated secretory phenotype (SASP). The senescence biomarker p16INK4a is a potent inhibitor of the cell cycle but is not essential for SASP production. Thus, it is unclear whether p16INK4a identifies senescence in hyporeplicative cells such as articular chondrocytes and whether p16INK4a contributes to pathologic characteristics of cartilage aging. To address these questions, we examined the role of p16INK4a in murine and human models of chondrocyte aging. We observed that p16INK4a mRNA expression was significantly upregulated with chronological aging in murine cartilage (~50-fold from 4 to 18 months of age) and in primary human chondrocytes from 57 cadaveric donors (r2  = .27, p < .0001). Human chondrocytes exhibited substantial replicative potential in vitro that depended on the activity of cyclin-dependent kinases 4 or 6 (CDK4/6), and proliferation was reduced in cells from older donors with increased p16INK4a expression. Moreover, increased chondrocyte p16INK4a expression correlated with several SASP transcripts. Despite the relationship between p16INK4a expression and these features of senescence, somatic inactivation of p16INK4a in chondrocytes of adult mice did not mitigate SASP expression and did not alter the rate of osteoarthritis (OA) with physiological aging or after destabilization of the medial meniscus. These results establish that p16INK4a expression is a biomarker of dysfunctional chondrocytes, but that the effects of chondrocyte senescence on OA are more likely driven by production of SASP molecules than by loss of chondrocyte replicative function.

Identification of novel MyoD gene targets in proliferating myogenic stem cells.

A major control point for skeletal myogenesis revolves around the muscle basic helix-loop-helix gene family that includes MyoD, Myf-5, myogenin, and MRF4. Myogenin and MRF4 are thought to be essential to terminal differentiation events, whereas MyoD and Myf-5 are critical to establishing the myogenic cell lineage and producing committed, undifferentiated myogenic stem cells (myoblasts). Although mouse genetic studies have revealed the importance of MyoD and Myf-5 for myoblast development, the genetic targets of MyoD and Myf-5 activity in undifferentiated myoblasts remain unknown. In this study, we investigated the function of MyoD as a transcriptional activator in undifferentiated myoblasts. By using conditional expression of MyoD, in conjunction with suppression subtractive hybridizations, we show that the Id3 and NP1 (neuronal pentraxin 1) genes become transcriptionally active following MyoD induction in undifferentiated myoblasts. Activation of Id3 and NP1 represents a stable, heritable event that does not rely on continued MyoD activity and is not subject to negative regulation by an activated H-Ras G12V protein. These results are the first to demonstrate that MyoD functions as a transcriptional activator in myogenic stem cells and that this key myogenic regulatory factor exhibits different gene target specificities, depending upon the cellular environment.

Cellular Senescence Promotes Adverse Effects of Chemotherapy and Cancer Relapse.

Cellular senescence suppresses cancer by irreversibly arresting cell proliferation. Senescent cells acquire a proinflammatory senescence-associated secretory phenotype. Many genotoxic chemotherapies target proliferating cells nonspecifically, often with adverse reactions. In accord with prior work, we show that several chemotherapeutic drugs induce senescence of primary murine and human cells. Using a transgenic mouse that permits tracking and eliminating senescent cells, we show that therapy-induced senescent (TIS) cells persist and contribute to local and systemic inflammation. Eliminating TIS cells reduced several short- and long-term effects of the drugs, including bone marrow suppression, cardiac dysfunction, cancer recurrence, and physical activity and strength. Consistent with our findings in mice, the risk of chemotherapy-induced fatigue was significantly greater in humans with increased expression of a senescence marker in T cells prior to chemotherapy. These findings suggest that senescent cells can cause certain chemotherapy side effects, providing a new target to reduce the toxicity of anticancer treatments. SIGNIFICANCE: Many genotoxic chemotherapies have debilitating side effects and also induce cellular senescence in normal tissues. The senescent cells remain chronically present where they can promote local and systemic inflammation that causes or exacerbates many side effects of the chemotherapy. Cancer Discov; 7(2); 165-76. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 115.

RAS and the RAIN/RasIP1 effector.

Ras proteins function as signaling nodes that are activated by extracellular stimuli. On activation, Ras interacts with a spectrum of functionally diverse downstream effectors and stimulates a variety of downstream cytoplasmic signaling cascades that regulate cellular proliferation, differentiation, and apoptosis. In addition to the association of Ras with the plasma membrane, recent studies have established an association of Ras with Golgi membranes and showed that H-Ras and N-Ras are activated on endomembranes and signal to regulate downstream pathways. Whereas the effectors of signal transduction by activated, plasma membrane-localized Ras are well characterized, very little is known about the effectors used by Golgi-associated Ras. Recently, we have reported the identification of the first endomembrane Ras effector molecule, RAIN. This chapter details the methods used to study RAIN-Ras interaction and localization in vivo. In addition, we describe the tools and methods we have used to explore role of endogenous RAIN in endothelial cells.

Chemotherapy and Stem Cell Transplantation Increase p16INK4a Expression, a Biomarker of T-cell Aging.

The expression of markers of cellular senescence increases exponentially in multiple tissues with aging. Age-related physiological changes may contribute to adverse outcomes in cancer survivors. To investigate the impact of high dose chemotherapy and stem cell transplantation on senescence markers in vivo, we collected blood and clinical data from a cohort of 63 patients undergoing hematopoietic cell transplantation. The expression of p16INK4a, a well-established senescence marker, was determined in T-cells before and 6months after transplant. RNA sequencing was performed on paired samples from 8 patients pre- and post-cancer therapy. In patients undergoing allogeneic transplant, higher pre-transplant p16INK4a expression was associated with a greater number of prior cycles of chemotherapy received (p=0.003), prior autologous transplantation (p=0.01) and prior exposure to alkylating agents (p=0.01). Transplantation was associated with a marked increase in p16INK4a expression 6months following transplantation. Patients receiving autologous transplant experienced a larger increase in p16INK4a expression (3.1-fold increase, p=0.002) than allogeneic transplant recipients (1.9-fold increase, p=0.0004). RNA sequencing of T-cells pre- and post- autologous transplant or cytotoxic chemotherapy demonstrated increased expression of transcripts associated with cellular senescence and physiological aging. Cytotoxic chemotherapy, especially alkylating agents, and stem cell transplantation strongly accelerate expression of a biomarker of molecular aging in T-cells.

Rho GTPase Transcriptome Analysis Reveals Oncogenic Roles for Rho GTPase-Activating Proteins in Basal-like Breast Cancers.

The basal-like breast cancer (BLBC) subtype accounts for a disproportionately high percentage of overall breast cancer mortality. The current therapeutic options for BLBC need improvement; hence, elucidating signaling pathways that drive BLBC growth may identify novel targets for the development of effective therapies. Rho GTPases have previously been implicated in promoting tumor cell proliferation and metastasis. These proteins are inactivated by Rho-selective GTPase-activating proteins (RhoGAP), which have generally been presumed to act as tumor suppressors. Surprisingly, RNA-Seq analysis of the Rho GTPase signaling transcriptome revealed high expression of several RhoGAP genes in BLBC tumors, raising the possibility that these genes may be oncogenic. To evaluate this, we examined the roles of two of these RhoGAPs, ArhGAP11A (also known as MP-GAP) and RacGAP1 (also known as MgcRacGAP), in promoting BLBC. Both proteins were highly expressed in human BLBC cell lines, and knockdown of either gene resulted in significant defects in the proliferation of these cells. Knockdown of ArhGAP11A caused CDKN1B/p27-mediated arrest in the G1 phase of the cell cycle, whereas depletion of RacGAP1 inhibited growth through the combined effects of cytokinesis failure, CDKN1A/p21-mediated RB1 inhibition, and the onset of senescence. Random migration was suppressed or enhanced by the knockdown of ArhGAP11A or RacGAP1, respectively. Cell spreading and levels of GTP-bound RhoA were increased upon depletion of either RhoGAP. We have established that, via the suppression of RhoA, ArhGAP11A and RacGAP1 are both critical drivers of BLBC growth, and propose that RhoGAPs can act as oncogenes in cancer. Cancer Res; 76(13); 3826-37. ©2016 AACR.