Abstract 2468: ATM signaling to mTORC1 in response to DNA damage independent of AMPK activation

When DNA becomes damaged either as a result of endogenous processes or exposure to radiation or chemicals, the DNA damage response is rapidly engaged. DNA damage response pathways have been well-characterized at the molecular level, and are known to involve a large network of proteins that trigger cell cycle checkpoints to allow time for DNA repair or trigger apoptosis via p53-dependent mechanisms if the damage is too severe to be repaired. However in addition to these classic damage responses, our previous work on ROS-induced pathways indicated that an additional aspect of the cellular damage response to many types of damage or stress could be induction of autophagy via repression of mTORC1.

We found previously that ROS could activate ATM in the cytoplasm, independently of the DNA damage produced by ROS, and subsequently activate the LKB1-AMPK energy-sensing pathway to activate TSC2 and repress mTOR, therefore inducing autophagy. We next asked whether a similar pathway could be induced in response to DNA damage, since there have been a few reports of AMPK activation by DNA damage in some cell lines, and ATM has been shown to activate AMPK via both LKB1-dependent and LKB1-independent mechanisms.

In a panel of cancer cell lines, including MCF7 breast carcinoma cells and SKOV3 ovarian carcinoma and other cells such as MEFs and HEK293, we profiled the signaling events in response to classic double-strand break agents such as etoposide, ionizing radiation or radiomimetic neocarzinostatin, as well as the intrastrand crosslinking agent cisplatin. In a cell-line and damage-specific manner, mTORC1 could be repressed, but unlike the previously identified ROS-induced signaling pathway, AMPK was not activated. In addition, in contrast to the rapid ROS-induced signaling pathway, DNA damage induced mTORC1 suppression occurred over a period of hours (6-24 hours), suggesting that additional mechanisms may be involved in signaling to mTORC1. Using Tsc2-deficient MEFs, we demonstrated that mTORC1 suppression requires TSC2, a negative regulator of mTORC1. This dichotomous response between ROS-induced mTORC1 suppression via AMPK activation of TSC2, and DNA damage, which does not require AMPK, indicates that mTORC1 regulation by DNA damage is complex and context-dependent, which may have implications for understanding mechanisms of action of DNA damaging cancer therapeutics.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2468. doi:10.1158/1538-7445.AM2011-2468

The role of LKB1 and AMPK in cellular responses to stress and damage

The LKB1 and AMPK proteins participate in an energy sensing cascade that responds to depletion of ATP, serving as a master regulator of metabolism that inhibits anabolic processes and stimulates catabolic processes. However in recent years, LKB1 and AMPK have been implicated in a variety of other cellular processes, both cytoplasmic and nuclear, such as control of cell polarity and regulation of gene transcription. In this review, we summarize the most recent discoveries regarding participation of LKB1 and AMPK in signaling pathways that respond to cellular stress and damage, and the relevance of this signaling for disease and therapy.

Wiltshire pharmacy health promotion training initiative: a telephone survey

A telephone survey of 40 pharmacists before and after attendance on a health promotion course in Wiltshire, conducted using semi-structured questionnaires, indicated that training led to changes in knowledge and perceived changes in attitude and practice. The value of the increased knowledge was recognised by participants, in particular when talking to patients and other health professionals. The change in attitude, towards a more holistic view of health, is seen by the authors as a positive benefit of training, as it may be of value to the pharmacists. Changes in practice were evident despite recognised constraints.

Recommendations for future health promotion training schemes are: training should be ongoing; joint working with other health care professionals is needed fully to achieve training objectives; the role of the pharmacist should be promoted; and this currently unremunerated role should be recognised by Wiltshire health authority for its potential contribution towards the health care of the population, and receive appropriate funding.

Response to dysmenorrhoea: An assessment of pharmacists' knowledge and its application in practice

A combination of covert participant observation and semi-structured interviews was used in 65 pharmacies to assess pharmacists' skills and knowledge in their response to the symptom of dysmenorrhoea. The pharmacists were found to ask too few questions; 12 per cent asked no questions. Over half the pharmacists did not recommend the product of choice. Few pharmacists adopted a structured approach when responding to the symptom. The disappointing results could relate to a number of factors, one of which, inadequate training, was cited in the interviews.

Abstract P1-10-02: A Novel Attempt To Improve Long-Term Patient Follow-Up in a Low Resource Urban Setting

The lack of either a nationalized health care structure or widespread health insurance in most developing nations is at the root of many of our health care challenges. Amongst them is the loss to follow-up of a majority of patients treated at tertiary care centers. As a consequence, outcomes data from such countries are notoriously non representative. While there have been numerous published reports of treatment outcomes of cancers from India, the reported numbers as a proportion of originally treated patients are probably less than half. We have attempted a simple solution to this problem, made possible primarily by the revolution of low cost mobile cell phones and almost universal access.

Methods.

St. John's Medical College Hospital is a tertiary care centre located in Bangalore, India. We established a patient support group called Aadhara (“Support” in Sanskrit). Aadhara has employed two women with training in counseling and clinical research. Both were provided with cell phones. At the time of initial breast cancer diagnosis, patients are enrolled in a long term follow-up study. Cell phone numbers, address and other contact details of patients and/or next of kin are obtained. The patients and their family are informed about the psycho-social support available at Aadhara that include counseling, psycho-education, talks on psycho-social aspects of the disease, nutrition, news letters, meeting long-term survivors and community breast cancer awareness programs. They are provided phone numbers and email ids to get in touch with the counselors as needed. The patients or their family are contacted by the counselors on a monthly basis. However the patients are free to get in touch with the counselors by just making a “missed call” to the cell phone numbers.

Results

Aadhara has been operational for close to two years. During this period we have enrolled 121 patients into our longitudinal observational study. There have been 11 deaths in our cohort. The most gratifying outcome has been the loss of only 2 patients to follow-up. This represents a greater than 95% follow-up. The costs of this entire program have been made available by a philanthropic organization and are approximately USD 2000 per month. Represented as per patient cost, this is less than USD 20/patient per month and could probably be halved as the enrollments grow. Discussion

The rapid and deep penetration of mobile phone services in India present opportunities for obtaining better metrics of the consequences of medical treatment. This model has the advantage of scalability and diminishing per patient costs as the numbers grow. It is also portable to other clinical conditions where long-term outcomes are needed to guide health care interventions. This is “proof-of-concept” that improved outcome measures can be obtained in low resource settings at costs that are a fraction of the cost of treatment.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-10-02.

Differential localization of ATM is correlated with activation of distinct downstream signaling pathways

ATM, the gene mutated in the genetic disease ataxia telangiectasia (AT), is a well-known protein involved in the DNA double-strand break response, where it plays an important role in sensing damage and signaling to DNA repair machinery and cell cycle checkpoints. However, a number of recent papers, including ours have found that ATM also plays important roles outside of the nucleus, which may explain some of the phenotypic features seen in AT patients. Our research into mechanisms of TSC2 regulation helped uncover a pathway upstream of TSC2 that is regulated by cytoplasmic ATM in response to ROS initiated by ATM activation of LKB1 and AMPK. We found that TSC2 activation results in mTORC1 repression and subsequent induction of autophagy. Elucidation of this stress response pathway provides a molecular mechanism for ATM signaling in the cytoplasm and lays the groundwork for further studies on how ATM activity is regulated beyond DNA damage in different cellular compartments.

Prenatal cocaine exposure increases anxiety, impairs cognitive function and increases dendritic spine density in adult rats: influence of sex

Cocaine exposure during pregnancy can impact brain development and have long-term behavioral consequences. The present study examined the lasting consequences of prenatal cocaine (PN-COC) exposure on the performance of cognitive tasks and dendritic spine density in adult male and female rats. From gestational day 8 to 20, dams were treated daily with 30 mg/kg (ip) of cocaine HCl or saline. At 62 days of age, offspring were tested consecutively for anxiety, locomotion, visual memory and spatial memory. PN-COC exposure significantly increased anxiety in both sexes. Object recognition (OR) and placement (OP) tasks were used to assess cognitive function. Behavioral tests consisted of an exploration trial (T1) and a recognition trial (T2) that were separated by an inter-trial delay of varying lengths. Male PN-COC subjects displayed significantly less time investigating new objects or object locations during T2 in both OR and OP tasks. By contrast, female PN-COC subjects exhibited impairments only in OR and only at the longest inter-trial delay interval. In addition, gestational cocaine increased dendritic spine density in the prefrontal cortex and nucleus accumbens in both genders, but only females had increased spine density in the CA1 region of the hippocampus. These data reveal that in-utero exposure to cocaine results in enduring alterations in anxiety, cognitive function and spine density in adulthood. Moreover, cognitive deficits were more profound in males than in females.

ATM engages the TSC2/mTORC1 signaling node to regulate autophagy

The link between reactive oxygen species (ROS) and induction of autophagy has been well documented, but the molecular mechanisms regulating this phenomenon are only beginning to be elucidated. Autophagy is now being appreciated as an integral part of the cellular response to many diverse types of cellular stresses including nutrient deprivation, hypoxia, oxidative stress, and DNA damage, and likely the mechanism(s) for each type of stress vary considerably. The cellular outcome of inducing autophagy in response to stress is also quite complex, and depends on many factors including cellular context, type and magnitude of stress.

Abstract 4831: ATM signals to TSC2 in the cytoplasm to regulate mTORC1 and autophagy in response to ROS

ATM is a cellular damage sensor that coordinates the cell cycle with damage-response checkpoints and DNA repair to preserve genomic integrity. ATM deficiency is also associated with increased oxidative stress, and ATM has been implicated in metabolic regulation. The mechanisms responsible for crosstalk between oxidative stress and metabolic pathways are not fully understood, but are important since tumors often exhibit elevated ROS, and redox pathways may be therapeutic targets.

We report a novel cytoplasmic pathway whereby ATM activates the TSC2 tumor suppressor, via LKB1 and AMPK in response to ROS, distinct from that of nuclear ATM in the DNA damage response. Knockout MEFs and siRNA approaches illustrated that mTORC1 suppression by ROS was dependent upon Tsc2 and ATM, and independent of p53. Reconstitution of LKB1-deficient HeLa S3 cells with wild-type LKB1 restored mTORC1 repression by ROS, while reconstitution of a mutant LKB1 lacking the ATM phosphorylation site did not. An in vivo cell-based functional assay revealed that a Tsc2 mutant lacking AMPK phosphorylation sites was deficient in repressing mTORC1 activity in response to H202, directly implicating AMPK as the mediator of ATM signaling to Tsc2. We also demonstrated that ATM activation of the LKB1-AMPK pathway was responsible for TSC2-mediated mTORC1 repression exclusively in the cytoplasm with subcellular fractionation and leptomycin B.

Importantly, elevated ROS and dysregulation of mTORC1 in both ATM-deficient and Tsc2-deficient cells was inhibited with rapamycin. We also show for that rapamycin rescued lymphomagenesis in Atm-deficient mice, resulting in enhanced survival.

mTORC1 negatively regulates autophagy, a cellular process which degrades organelles and long-lived proteins as a survival mechanism, but can also cause cell death. We tested the hypothesis that repression of mTORC1 by ROS results in induction of autophagy. Electron microscopy analysis demonstrated enhanced formation of autophagosomes in response to ROS. In MCF7 and SKOV-3 cells stably expressing GFP-LC3, a marker of autophagosomes, we observed an increase in punctate GFP-labeled autophagosomes, consistent with autophagy induction. A necessary step during autophagosome formation is lipidation of the cytosolic form of LC3 (LC3 I) to LC3 II, which can be detected as a mobility shift by western analysis. Western analysis confirmed that LC3 II was increased, and concomitantly, the autophagic substrate p62 was decreased, in response to ROS-mediated mTORC1 repression.

Together, our results identify a pathway for ATM activation of TSC2 to regulate mTORC1 signaling and autophagy in response to ROS, identifying a new integration node for the cellular damage response with key pathways involved in metabolism, protein synthesis, and cell survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4831.

Deer velvet supplementation decreases the grade and metastasis of azoxymethane-induced colon cancer in the male rat

Since deer velvet (DV) extract promotes angiogenesis, its ability to modulate the growth and invasiveness of colon tumours was investigated. Male Wistar rats were each given a subcutaneous injection of azoxymethane (AOM) at 15 mg/kg once a week for 3 weeks. One week following the last dose of AOM the rats received either 1g/kg of DV delivered in a cube of raspberry gelatin or plain raspberry gelatin daily for 26 weeks. At necropsy, tumours were measured and the distance from the anus was recorded. Tissue samples were categorised according to the Astler-Coller system. The results showed that there were no significant differences in most parameters examined (i.e. body weight gain, multiplicity, tumour volume and incidence). The only statistically significant differences seen were associated with metastasis and tumour grade. Specifically, more of the tumours in the DV-treated rats were of a lower grade compared to the controls, both when all tumour sites were considered (0.91 vs. 0.66, p<0.0001), as well as those located only in the colon (0.95 vs. 0.84, p<0.03). Therefore, this study can confidently conclude that DV does not increase the incidence, multiplicity, metastasis or tumour volume of AOM-induced colon cancer in the rat.

PTEN deficiency is fully penetrant for prostate adenocarcinoma in C57BL/6 mice via mTOR-dependent growth

The tumor suppressor phosphatase and tensin homolog (PTEN) is frequently involved in human prostate carcinoma. PTEN is therefore an attractive target for the development of preclinical animal models. Prostate intraepithelial neoplasia lesions develop in mice with Pten heterozygosity, but disease progression has been reported only in combination with either other tumor suppressor gene alterations or the conditional inactivation of both Pten alleles in prostate epithelial cells. We report that on a C57BL/6 background, in contrast to previous studies on mixed 129 genetic backgrounds, Pten locus heterozygosity is fully penetrant for the development of prostate adenocarcinoma. Grossly observable tumors were detected at 6 months of age, and, by 10 to 12 months, 100% of examined mice developed adenocarcinoma of the anterior prostate. Furthermore, double heterozygotes carrying both Pten and Tsc2-null alleles showed no increase relative to Pten(+/-) heterozygotes in either lesion development or progression. Lesions in both Pten(+/-); Tsc2(+/-), and Pten(+/-) mice exhibited loss of PTEN expression and activation of PI3K signaling. PI3K activation occurred early in prostate intraepithelial neoplasia lesion formation in these animals, consistent with loss of PTEN function, and contributed to the etiology of tumors that developed in Pten(+/-) mice. Furthermore, prostate lesion growth in Pten(+/-) mice was dependent on mTOR, as evidenced by a reduction in both phospho-S6 levels and proliferative index after rapamycin treatment.

Cytoplasmic sequestration of p27 via AKT phosphorylation in renal cell carcinoma

PURPOSE

p27 localization and expression has prognostic and predictive value in cancer. Little is known regarding expression patterns of p27 in renal cell carcinoma (RCC) or how p27 participates in disease progression or response to therapy.

EXPERIMENTAL DESIGN

RCC-derived cell lines, primary tumors, and normal renal epithelial cells were analyzed for p27 expression, phosphorylation (T157 of the NLS), and subcellular localization. RCC-derived cell lines were treated with phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors and effects on p27 localization were assessed. The potential contribution of cytoplasmic p27 to resistance to apoptosis was also evaluated.

RESULTS

p27 was elevated in tumors compared with matched controls, and cytoplasmic mislocalization of p27 was associated with increasing tumor grade. Cytoplasmic localization of p27 correlated with phosphorylation at T157, an AKT phosphorylation site in the p27 NLS. In RCC cell lines, activated PI3K/AKT signaling was accompanied by mislocalization of p27. AKT activation and phosphorylation of p27 was associated with resistance to apoptosis, and small interfering RNA knockdown of p27 or relocalization to the nucleus increased apoptosis in RCC cells. Treatment with the PI3K inhibitors LY294002 or wortmannin resulted in nuclear relocalization of p27, whereas mTOR inhibition by rapamycin did not.

CONCLUSIONS

In RCC, p27 is phosphorylated at T157 of the NLS, with increasing tumor grade associated with cytoplasmic p27. PI3K inhibition (which reduces AKT activity) reduces T157 phosphorylation and induces nuclear relocalization of p27, whereas mTOR inhibition does not. Clinical testing of these findings may provide a rational approach for use of mTOR and PI3K/AKT pathway inhibitors in patients with RCC.