PlexinB1 Promotes Nuclear Translocation of the Glucocorticoid Receptor

Synergistic combination of isogarcinol isolated from edible fruits of Garcinia multiflora and dexamethasone to overcome leukemia glucocorticoid resistance

Isogarcinol (ISO), a cytotoxic polycyclic polyprenylated acylphloroglucinol isolated from the edible fruits of Garcinia multiflora. However, synergistic combination of ISO and dexamethasone (DEX) to overcome leukemia glucocorticoid resistance has never been investigated. Therefore, in this study, the effects of ISO in combination with DEX was conducted on leukemia in vivo and glucocorticoid resistance in vitro. As a result, the combination of the two compounds could efficiently inhibit leukemia progression in mice and reverse DEX resistance in acute lymphoblastic leukemia (ALL) Jurkat cells. Significantly, our findings indicated that c-Myc may be a potential target of ISO, as it is involved in cell cycle arrest and apoptosis by the combination of ISO and DEX in Jurkat cells. Furthermore, western blot analysis revealed that ISO and DEX inhibits the PI3K/Akt/mTOR signaling pathway and promotes the nuclear translocation of glucocorticoid receptor (GR), which activates target genes NR3C1 and TSC22D3, leading to apoptosis in Jurkat cells. Hence, our results suggest that ISO, as a safe and effective food-derived agent, can enhance the anti-leukemia effects of DEX.

B-type Plexins promote the GTPase activity of Ran to affect androgen receptor nuclear translocation in prostate cancer

Resistance to anti-androgen therapy for metastatic prostate cancer is a major clinical problem. Sema3C promotes resistance to androgen withdrawal via its receptor, PlexinB1. Activation of PlexinB1 promotes the ligand-independent nuclear translocation of the androgen receptor (AR), which may contribute to resistance to androgen deprivation therapy. However, the mechanism by which PlexinB1 promotes nuclear translocation is unclear. We show here that PlexinB1 and B2 regulate nuclear import by acting as GTPase activating proteins (GAPs) for the small RasGTPase Ran, a key regulator of nuclear trafficking. Purified PlexinB1/B2 protein catalyses the hydrolysis of RanGTP, and mutations in the GAP domain of PlexinB1 inhibit this activity. Activation of PlexinB1/B2 with Sema4D decreases the levels of RanGTP, while PlexinB1 or B2 depletion increases the levels of activated Ran in the cell. Ran directly associates with B-type plexins in a GTP-dependent manner. Sema4D is internalised by endocytosis, and PlexinB1 and Ran display overlapping patterns of expression. Furthermore, Sema4D/PlexinB1-induced AR nuclear translocation is dependent on the GAP domain of PlexinB1 and is blocked by the expression of non-functional Ran mutants. Depletion of PlexinB1 decreases the nuclear/cytoplasmic ratio of Ran, indicative of a higher RanGTP/GDP ratio. Plexins may promote the growth of androgen-independent prostate cancer through their activity as RanGAPs.

Genomic and non-genomic effects of glucocorticoids in respiratory diseases

Cortisol is an endogenous steroid hormone essential for the natural resolution of inflammation. Synthetic glucocorticoids (GCs) were developed and are currently amongst the most widely prescribed anti-inflammatory drugs in our modern clinical landscape owing to their potent anti-inflammatory activity. However, the extent of GC's effects has yet to be fully elucidated. Indeed, GCs modulate a broad spectrum of cellular activity, from their classical regulation of gene expression to acute non-genomic mechanisms of action. Furthermore, tissue specific effects, disease specific conditions, and dose-dependent responses complicate their use, with side-effects potentially plaguing their use. It is thus vital to outline and consolidate the effects of GCs, to demystify and maximize their therapeutic potential while avoiding pitfalls that would otherwise render them obsolete.

Plexin-B1 Mutation Drives Metastasis in Prostate Cancer Mouse Models

Metastatic prostate cancer is essentially incurable and is a leading cause of cancer-related morbidity and mortality in men, yet the underlying molecular mechanisms are poorly understood. Plexins are transmembrane receptors for semaphorins with divergent roles in many forms of cancer. We show here that prostate epithelial cell-specific expression of a mutant form of Plexin-B1 (P1597L) which was identified in metastatic deposits in patients with prostate cancer, significantly increases metastasis, in particular metastasis to distant sites, in two transgenic mouse models of prostate cancer (PbCre⁺Pten^{fl /fl}Kras^G12V and PbCre⁺Pten^{fl /fl}p53^{fl/ fl} ). In contrast, prostate epithelial cell-specific expression of wild-type (WT) Plexin-B1 in PbCre⁺Pten^{fl /fl}Kras^G12V mice significantly decreases metastasis, showing that a single clinically relevant Pro1597Leu amino-acid change converts Plexin-B1 from a metastasis-suppressor to a metastasis-promoter. Furthermore, PLXNB1^P1597L significantly increased invasion of tumor cells into the prostate stroma, while PLXNB1^WT reduced invasion, suggesting that Plexin-B1 has a role in the initial stages of metastasis. Deletion of RhoA/C or PDZRhoGEF in Pten^{fl /fl}Kras^G12VPLXNB1^P1597L mice suppressed metastasis, implicating the Rho/ROCK pathway in this phenotypic switch. Germline deletion of Plexin-B1, to model anti-Plexin-B1 therapy, significantly decreased invasion and metastasis in both models. Our results demonstrate that Plexin-B1 plays a complex yet significant role in metastasis in mouse models of prostate cancer and is a potential therapeutic target to block the lethal spread of the disease.

Significance

Few therapeutic targets have been identified specifically for preventing locally invasive/oligometastatic prostate cancer from becoming more widely disseminated. Our findings suggest Plexin-B1 signaling, particularly from the clinically relevant P1597L mutant, is such a target.

Class IV semaphorins in disease pathogenesis

Semaphorins are a large family of secreted and/or transmembrane proteins, originally identified as proteins that function in axon guidance during neuronal development. However, semaphorins play crucial roles in other physiological and pathological processes, including immune responses, angiogenesis, maintenance of tissue homeostasis, and cancer progression. Class IV semaphorins may be present as transmembrane and soluble forms and are implicated in the pathogenesis of various diseases. This review discusses recent progress on the roles of class IV semaphorins determined by clinical and experimental pathology studies.

Generalized and tissue specific glucocorticoid resistance

Glucocorticoids (GCs) are steroid hormones that influence several physiologic functions and are among the most frequently prescribed drugs worldwide. Resistance to GCs has been observed in the context of the familial generalized GC resistance (Chrousos' syndrome) or tissue specific GC resistance in chronic inflammatory states. In this review, we have summarized the major factors that influence individual glucocorticoid sensitivity/resistance. The fine-tuning of GC action is determined in a tissue-specific fashion that includes the combination of different GC receptor promoters, translation initiation sites, splice isoforms, interacting proteins, post-translational modifications, and alternative mechanisms of signal transduction.

Psychosocial Stress, Glucocorticoid Signaling, and Prostate Cancer Health Disparities in African American Men

Recent advances in our understanding of racial disparities in prostate cancer (PCa) incidence and mortality that disproportionately affect African American (AA) men have provided important insights into the psychosocial, socioeconomic, environmental, and molecular contributors. There is, however, limited mechanistic knowledge of how the interplay between these determinants influences prostate tumor aggressiveness in AA men and other men of African ancestry. Growing evidence indicates that chronic psychosocial stress in AA populations leads to sustained glucocorticoid signaling through the glucocorticoid receptor (GR), with negative physiological and pathological consequences. Compelling evidence indicates that treatment of castration-resistant prostate cancer (CRPC) with anti-androgen therapy activates GR signaling. This enhanced GR signaling bypasses androgen receptor (AR) signaling and transcriptionally activates both AR-target genes and GR-target genes, resulting in increased prostate tumor resistance to anti-androgen therapy, chemotherapy, and radiotherapy. Given its enhanced signaling in AA men, GR-together with specific genetic drivers-may promote CRPC progression and exacerbate tumor aggressiveness in this population, potentially contributing to PCa mortality disparities. Ongoing and future CRPC clinical trials that combine standard of care therapies with GR modulators should assess racial differences in therapy response and clinical outcomes in order to improve PCa health disparities that continue to exist for AA men.