PI3K Functions Downstream of Cdc42 to Drive Cancer phenotypes in a Melanoma Cell Line

Rho proteins are part of the Ras superfamily, which function to modulate cytoskeletal dynamics including cell adhesion and motility. Recently, an activating mutation in Cdc42, a Rho family GTPase, was found in a patient sample of melanoma. Previously, our work had shown the PI3K was important downstream of mutationally active Cdc42. Our present study sought to determine whether PI3K was a crucial downstream partner for Cdc42 in a melanoma cells line with a BRAF mutation, which is the most common mutation in cutaneous melanoma. In this work we were able to show that Cdc42 contributes to proliferation, anchorage-independent growth, cell motility and invasion. Treatment with a pan-PI3K inhibitor was able to effectively ameliorate all these cancer phenotypes. These data suggest that PI3K may be an important target downstream of Cdc42 in melanoma.

A Novel Approach to Addiction Medicine Education for Undergraduate Medical Students

A virtual addiction medicine elective was developed using interactive multimedia modules, active learning strategies, and patient-based cases. Student had opportunities for professional networking and interacting with physicians and patients. The elective was successful in boosting Year-1 medical students' confidence to screen, manage, and treat patients with substance abuse disorder.

Quantitative Profiling Method for Oxylipins in Neurodegenerative Diseases by Liquid Chromatography Coupled with Tandem Mass Spectrometry

Aging is one of the major risk factors for many chronic diseases, including diabetes, neuropathy, hypertension, cancer, and neurodegenerative diseases. However, the mechanism behind aging and how aging affects a variety of disease progression remains unknown. Recent research demonstrated the cytochrome P450 (CYP)-epoxide hydrolase (EH) metabolites of polyunsaturated fatty acids (PUFAs) play a critical role in the abovementioned age-associated diseases. Therefore, aging could affect the abovementioned chronic diseases by modulating CYP-EH PUFA metabolism. Unfortunately, investigating how aging affects CYP-EH metabolism in human and mammalian models poses significant challenges. In this regard, we will use C. elegans as a model organism to investigate the aging effects on CYP-EH metabolism of PUFA, owing to its long history of being used to study aging and its associated benefits of conducting aging research. This project will develop analytical tools to measure the endogenous levels of CYP-EH PUFA metabolites in C. elegans using state-of-the-art ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). These metabolites are very potent but present in low abundance. The dramatic increase in sensitivity in UPLC-MS/MS allows us to monitor these metabolites over the lifespan of C. elegans with minimum samples. Our results show that C. elegans produces similar CYP PUFA metabolites to mammals and humans using our SPE-UPLC-MS/MS method. We will also show that our method successfully determined the CYP-EH PUFA metabolites profile changes induced by the inhibition of C. elegans EH. The method developed from this project will significantly improve our understanding of the role of dietary PUFAs and associated metabolism on aging and neurodegeneration and will uncover new mechanisms of how aging affects neurodegeneration through the modulation of PUFA metabolic pathways.

Cytochrome P450 and Epoxide Hydrolase Metabolites in Aβ and tau-induced Neurodegeneration: Insights from Caenorhabditis elegans

This study aims to uncover potent cytochrome P450 (CYP) and epoxide hydrolase (EH) metabolites implicated in Aβ and/or tau-induced neurodegeneration, independent of neuroinflammation, by utilizing Caenorhabditis elegans (C. elegans) as a model organism. Our research reveals that Aβ and/or tau expression in C. elegans disrupts the oxylipin profile, and epoxide hydrolase inhibition alleviates the ensuing neurodegeneration, likely through elevating the epoxy-to-hydroxy ratio of various CYP-EH metabolites. In addition, our results indicated that the Aβ and tau likely affect the CYP-EH metabolism of PUFA through different mechanism. These findings emphasize the intriguing relationship between lipid metabolites and neurodegenerations, in particular, those linked to Aβ and/or tau aggregation. Furthermore, our investigation sheds light on the crucial and captivating role of CYP PUFA metabolites in C. elegans physiology, opening up possibilities for broader implications in mammalian and human contexts.

The Atypical Rho GTPase CHW-1 Works with SAX-3/Robo To Mediate Axon Guidance in Caenorhabditis elegans

During development, neuronal cells extend an axon toward their target destination in response to a cue to form a properly functioning nervous system. Rho proteins, Ras-related small GTPases that regulate cytoskeletal organization and dynamics, cell adhesion, and motility, are known to regulate axon guidance. Despite extensive knowledge about canonical Rho proteins (RhoA/Rac1/Cdc42), little is known about the Caenorhabditis elegans (C. elegans) atypical Cdc42-like family members CHW-1 and CRP-1 in regards to axon pathfinding and neuronal migration. chw-1(Chp/Wrch) encodes a protein that resembles human Chp (Wrch-2/RhoV) and Wrch-1 (RhoU), and crp-1 encodes for a protein that resembles TC10 and TCL. Here, we show that chw-1 works redundantly with crp-1 and cdc-42 in axon guidance. Furthermore, proper levels of chw-1 expression and activity are required for proper axon guidance. When examining CHW-1 GTPase mutants, we found that the native CHW-1 protein is likely partially activated, and mutations at a conserved residue (position 12 using Ras numbering, position 18 in CHW-1) alter axon guidance and neural migration. Additionally, we showed that chw-1 genetically interacts with the guidance receptor sax-3 in PDE neurons. Finally, in VD/DD motor neurons, chw-1 works downstream of sax-3 to control axon guidance. In summary, this is the first study implicating the atypical Rho GTPases chw-1 and crp-1 in axon guidance. Furthermore, this is the first evidence of genetic interaction between chw-1 and the guidance receptor sax-3 These data suggest that chw-1 is likely acting downstream and/or in parallel to sax-3 in axon guidance.

Mutationally activated Rho GTPases in cancer

The Rho family of GTPases (members of the Ras superfamily) are best known for their roles in regulating cytoskeletal dynamics. It is also well established that misregulation of Rho proteins contributes to tumorigenesis and metastasis. Unlike Ras proteins, which are frequently mutated in cancer (around 30%), Rho proteins themselves are generally not found to be mutated in cancer. Rather, misregulation of Rho activity in cancer was thought to occur by overexpression of these proteins or by misregulation of molecules that control Rho activity, such as activation or overexpression of GEFs and inactivation or loss of GAPs or GDIs. Recent studies, enabled by next-generation tumor exome sequencing, report activating point mutations in Rho GTPases as driver mutations in melanoma, as well as breast, and head and neck cancers. The Rac1(P29L) mutation identified in these tumor studies was previously identified by our lab as an activating Rac mutation in C. elegans neuronal development, highlighting the conserved nature of this mutation. Furthermore, this finding supports the relevance of studying Rho GTPases in model organisms such as C. elegans to study the mechanisms that underlie carcinogenesis. This review will describe the recent findings that report activating Rho mutations in various cancer types, moving Rho GTPases from molecules misregulated in cancer to mutagenic targets that drive tumorigenesis.

Multiple cytoskeletal pathways and PI3K signaling mediate CDC-42-induced neuronal protrusion in C. elegans

Rho GTPases are key regulators of cellular protrusion and are involved in many developmental events including axon guidance during nervous system development. Rho GTPase pathways display functional redundancy in developmental events, including axon guidance. Therefore, their roles can often be masked when using simple loss-of-function genetic approaches. As a complement to loss-of-function genetics, we constructed a constitutively activated CDC-42(G12V) expressed in C. elegans neurons. CDC-42(G12V) drove the formation of ectopic lamellipodial and filopodial protrusions in the PDE neurons, which resembled protrusions normally found on migrating growth cones of axons. We then used a candidate gene approach to identify molecules that mediate CDC-42(G12V)-induced ectopic protrusions by determining if loss of function of the genes could suppress CDC-42(G12V). Using this approach, we identified 3 cytoskeletal pathways previously implicated in axon guidance, the Arp2/3 complex, UNC-115/abLIM, and UNC-43/Ena. We also identified the Nck-interacting kinase MIG-15/NIK and p21-activated kinases (PAKs), also implicated in axon guidance. Finally, PI3K signaling was required, specifically the Rictor/mTORC2 branch but not the mTORC1 branch that has been implicated in other aspects of PI3K signaling including stress and aging. Our results indicate that multiple pathways can mediate CDC-42-induced neuronal protrusions that might be relevant to growth cone protrusions during axon pathfinding. Each of these pathways involves Rac GTPases, which might serve to integrate the pathways and coordinate the multiple CDC-42 pathways. These pathways might be relevant to developmental events such as axon pathfinding as well as disease states such as metastatic melanoma.

Analysis of Rho GTPase function in axon pathfinding using Caenorhabditis elegans

We provide information and protocols for the analysis of Rho GTPase function in axon pathfinding in Caenorhabditis elegans. The powerful molecular, genetic, imaging, and transgenic tools available in C. elegans make it an excellent system in which to study the in vivo roles of Rho GTPases. Methods for imaging of axon morphology in Rho GTPase single and double mutants are provided, as well as methods for the construction of transgenic C. elegans strains carrying exogenously introduced transgenes that drive the expression of constitutively active and dominant negative mutants.

RhoGDI2 antagonizes ovarian carcinoma growth, invasion and metastasis

Previous studies described functional roles for Rho GDP dissociation inhibitor 2 (RhoGDI2) in bladder, gastric and breast cancers. However, only limited expression and no functional analyses have been done for RhoGDI2 in ovarian cancer. We determined RhoGDI2 protein expression and function in ovarian cancer. First, protein gel blot analysis was performed to determine the expression levels of RhoGDI2 in ovarian cells lines. RhoGDI2 but not RhoGDI1 protein expression levels varied widely in ovarian carcinoma cell lines, with elevated levels seen in Ras-transformed ovarian epithelial cells. Next, immunohistochemistry was performed to detect RhoGDI2 expression in patient samples of ovarian cysts and ovarian cancer with known histological subtype, stage, grade and outcome. RhoGDI2 protein was significantly overexpressed in high-grade compared with low-grade ovarian cancers, correlated with histological subtype, and did not correlate with stage of ovarian cancer nor between carcinomas and benign cysts. Unexpectedly, stable suppression of RhoGDI2 protein expression in HeyA8 ovarian cancer cells increased anchorage-independent growth and Matrigel invasion in vitro and in tail-vein lung colony metastatic growth in vivo. Finally, we found that RhoGDI2 stably-associated preferentially with Rac1 and suppression of RhoGDI2 expression resulted in decreased Rac1 activity and Rac-associated JNK and p38 mitogenactivated protein kinase signaling. RhoGDI2 antagonizes the invasive and metastatic phenotype of HeyA8 ovarian cancer cells. In summary, our results suggest significant cell context differences in RhoGDI2 function in cancer cell growth.

Genetic and functional characterization of putative Ras/Raf interaction inhibitors in C. elegans and mammalian cells

Background

Activation of the mammalian Ras-Raf-MEK-ERK MAPK signaling cascade promotes cellular proliferation, and activating Ras mutations are implicated in cancer onset and maintenance. This pathway, a therapeutic target of interest, is highly conserved and required for vulval development in C. elegans. Gain-of-function mutations in the Ras ortholog lead to constitutive pathway signaling and a multivulva (Muv) phenotype. MCP compounds were identified in a yeast two-hybrid screen for their ability to disrupt Ras-Raf interactions. However, this had not been confirmed in another system, and conflicting results were reported regarding selective MCP-mediated blockade of Ras- and Raf-mediated biological activities in mammalian cells. Here we used the easily-scored Muv phenotype as an in vivo readout to characterize the selectivity of MCP110 and its analogs, and performed biochemical studies in mammalian cells to determine whether MCP treatment results in impaired interaction between Ras and its effector Raf.

Results

Our genetic analyses showed significant dose-dependent MCP-mediated reduction of Muv in C. elegans strains with activating mutations in orthologs of Ras (LET-60) or Raf (LIN-45), but not MAP kinases or an Ets-like transcription factor. Thus, these inhibitors selectively impair pathway function downstream of Ras and upstream of or at the level of Raf, consistent with disruption of the Ras/Raf interaction. Our biochemical analyses of MCP110-mediated disruption of Ras-Raf interactions in mammalian cells showed that MCP110 dose-dependently reduced Raf-RBD pulldown of Ras, displaced a fluorescently-tagged Raf-RBD probe from plasma membrane locations of active Ras to the cytosol and other compartments, and decreased active, phosphorylated ERK1/2.

Conclusions

We have effectively utilized C. elegans as an in vivo genetic system to evaluate the activity and selectivity of inhibitors intended to target the Ras-Raf-MAPK pathway. We demonstrated the ability of MCP110 to disrupt, at the level of Ras/Raf, the Muv phenotype induced by chronic activation of this pathway in C. elegans. In mammalian cells, we not only demonstrated MCP-mediated blockade of the physical interaction between Ras and Raf, but also narrowed the site of interaction on Raf to the RBD, and showed consequent functional impairment of the Ras-Raf-MEK-ERK pathway in both in vivo and cell-based systems.

Antagonism of neurosteroid modulation of native gamma-aminobutyric acid receptors by (3alpha,5alpha)-17-phenylandrost-16-en-3-ol

Endogenous pregnane neurosteroids are allosteric modulators at gamma-aminobutyric acid type-A (GABAA) receptors at nanomolar concentrations. There is direct evidence for multiple distinct neurosteroid binding sites on GABAA receptors, dependent upon subunit composition and stoichiometry. This view is supported by the biphasic kinetics of various neuroactive steroids, enantioselectivity of some neurosteroids, selective mutation studies of recombinantly expressed receptors and the selectivity of the neurosteroid antagonist (3alpha,5alpha)-17-phenylandrost-16-en-3-ol (17PA) on 5alpha-pregnane steroid effects on recombinant GABAA receptors expressed in Xenopus oocytes and native receptors in dissociated neurons. However, it is unclear whether this antagonist action is present in a mature mammalian system. The present study evaluated the antagonist activity of 17PA on neurosteroid agonists both in vivo and in vitro by examining the effects of 17PA on 5alpha-pregnane-induced sedation in rats, native mature GABAA receptor ion channels utilizing the chloride flux assay and further studies in recombinant alpha1beta2gamma2 receptors. The data show that 17PA preferentially inhibits 3alpha,5alpha-THP vs. alphaxalone in vivo, preferentially inhibits 3alpha,5alpha-THDOC vs. alphaxalone potentiation of GABA-mediated Cl- uptake in adult cerebral cortical synaptoneurosomes, but shows no specificity for 3alpha,5alpha-THDOC vs. alphaxalone in recombinant alpha1beta2gamma2 receptors. These data provide further evidence of the specificity of 17PA and the heterogeneity of neurosteroid recognition sites on GABAA receptors in the CNS.

Protein kinase C and epidermal growth factor stimulation of Raf1 potentiates adenylyl cyclase type 6 activation in intact cells

Adenylyl cyclase type 6 (AC6) activity is inhibited by protein kinase C (PKC) in vitro; however, in intact cells, PKC activation does not inhibit the activity of transiently expressed AC6. To investigate the effects of PKC activation on AC6 activity in intact cells, we constructed human embryonic kidney (HEK) 293 cells that stably express wild-type AC6 (AC6-WT) or an AC6 mutant lacking a PKC and cyclic AMP-dependent protein kinase (PKA) phosphorylation site, Ser674 (AC6-S674A). In contrast to in vitro observations, we observed a PKC-mediated enhancement of forskolin- and isoproterenol-stimulated cyclic AMP accumulation in HEK-AC6 cells. Phorbol 12-myristate 13-acetate also potentiated cyclic AMP accumulation in cells expressing endogenous AC6, including Chinese hamster ovary cells and differentiated Cath.a differentiated cells. In HEK-AC6-S674A cells, the potentiation of AC6 stimulation was significantly greater than in cells expressing AC6-WT. The positive effect of PKC activation on AC6 activity seemed to involve Raf1 kinase because the Raf1 inhibitor 3-(3,5-dibromo-4-hydroxybenzylidene-5-iodo-1,3-dihydro-indol-2-one (GW5074) inhibited the PKC potentiation of AC6 activity. Furthermore, the forskolin-stimulated activity of a recombinant AC6 in which the putative Raf1 regulatory sites have been eliminated was not potentiated by activation of PKC. The ability of Raf1 to regulate AC6 may involve a direct interaction because AC6 and a constitutively active Raf1 construct were coimmunoprecipitated. In addition, we report that epidermal growth factor receptor activation also enhances AC6 signaling in a Raf1-dependent manner. These data suggest that Raf1 potentiates drug-stimulated cyclic AMP accumulation in cells expressing AC6 after activation of multiple signaling pathways.