Mcl1 regulates the terminal mitosis of neural precursor cells in the mammalian brain through p27Kip1

Sevoflurane causes cognitive impairment by inducing iron deficiency and inhibiting the proliferation of neural precursor cells in infant mice

AIMS

Numerous studies on animals have shown that exposure to general anesthetics in infant stage may cause neurocognitive impairment. However, the exact mechanism is not clear. The dysfunction of iron metabolism can cause neurodevelopmental disorders. Therefore, we investigated the effect of iron metabolism disorder induced by sevoflurane (Sev) on cognitive function and the proliferation of neural precursor cells (NPCs) and neural stem cells (NSCs) in infant mice.

METHODS

C57BL/6 mice of postnatal day 14 and neural stem cells NE4C were treated with 2% Sev for 6 h. We used the Morris water maze (MWM) to test the cognitive function of infant mice. The proliferation of NPCs was measured using bromodeoxyuridine (BrdU) label and their markers Ki67 and Pax6 in infant brain tissues 12 h after anesthesia. Meanwhile, we used immunohistochemical stain, immunofluorescence assay, western blot, and flow cytometer to evaluate the myelinogenesis, iron levels, and cell proliferation in cortex and hippocampus or in NE4C cells.

RESULTS

The results showed that Sev significantly caused cognitive deficiency in infant mice. Further, we found that Sev inhibited oligodendrocytes proliferation and myelinogenesis by decreasing MBP and CC-1 expression and iron levels. Meanwhile, Sev also induced the iron deficiency in neurons and NSCs by downregulating FtH and FtL expression and upregulating the TfR1 expression in the cortex and hippocampus, which dramatically suppressed the proliferation of NSCs and NPCs as indicated by decreasing the colocalization of Pax6+ and BrdU+ cells, and caused the decrease in the number of neurons. Interestingly, iron supplementation before anesthesia significantly improved iron deficiency in cortex and hippocampus and cognitive deficiency induced by Sev in infant mice. Iron therapy inhibited the decrease of MBP expression, iron levels in neurons and oligodendrocytes, and DNA synthesis of Pax6+ cells in hippocampus induced by Sev. Meanwhile, the number of neurons was partially recovered in hippocampus.

CONCLUSION

The results from the present study demonstrated that Sev-induced iron deficiency might be a new mechanism of cognitive impairment caused by inhaled anesthetics in infant mice. Iron supplementation before anesthesia is an effective strategy to prevent cognitive impairment caused by Sev in infants.

Advances in in utero electroporation

In utero electroporation (IUE) is a technique developed in the early 2000s to transfect the neurons and neural progenitors of embryonic brains, thus enabling continued development in utero and subsequent analyses of neural development. Early IUE experiments focused on ectopic expression of plasmid DNA to analyze parameters such as neuron morphology and migration. Recent advances made in other fields, such as CRISPR/CAS9 genome editing, have been incorporated into IUE techniques as they were developed. Here, we provide a general review of the mechanics and techniques involved in IUE and explore the breadth of approaches that can be used in conjunction with IUE to study cortical development in a rodent model, with a focus on the novel advances in IUE techniques. We also highlight a few cases that exemplify the potential of IUE to study a broad range of questions in neural development.

Understanding MCL1: from cellular function and regulation to pharmacological inhibition

Myeloid cell leukemia-1 (MCL1), an antiapoptotic member of the BCL2 family characterized by a short half-life, functions as a rapid sensor that regulates cell death and other relevant processes that include cell cycle progression and mitochondrial homeostasis. In cancer, MCL1 overexpression contributes to cell survival and resistance to diverse chemotherapeutic agents; for this reason, several MCL1 inhibitors are currently under preclinical and clinical development for cancer treatment. However, the nonapoptotic functions of MCL1 may influence their therapeutic potential. Overall, the complexity of MCL1 regulation and function represent challenges to the clinical application of MCL1 inhibitors. We now summarize the current knowledge regarding MCL1 structure, regulation, and function that could impact the clinical success of MCL1 inhibitors.

Oligodendrocytes depend on MCL-1 to prevent spontaneous apoptosis and white matter degeneration

Neurologic disorders often disproportionately affect specific brain regions, and different apoptotic mechanisms may contribute to white matter pathology in leukodystrophies or gray matter pathology in poliodystrophies. We previously showed that neural progenitors that generate cerebellar gray matter depend on the anti-apoptotic protein BCL-xL. Conditional deletion of Bcl-xL in these progenitors produces spontaneous apoptosis and cerebellar hypoplasia, while similar conditional deletion of Mcl-1 produces no phenotype. Here we show that, in contrast, postnatal oligodendrocytes depend on MCL-1. We found that brain-wide Mcl-1 deletion caused apoptosis specifically in mature oligodendrocytes while sparing astrocytes and oligodendrocyte precursors, resulting in impaired myelination and progressive white matter degeneration. Disabling apoptosis through co-deletion of Bax or Bak rescued white matter degeneration, implicating the intrinsic apoptotic pathway in Mcl-1-dependence. Bax and Bak co-deletions rescued different aspects of the Mcl-1-deleted phenotype, demonstrating their discrete roles in white matter stability. MCL-1 protein abundance was reduced in eif2b5-mutant mouse model of the leukodystrophy vanishing white matter disease (VWMD), suggesting the potential for MCL-1 deficiency to contribute to clinical neurologic disease. Our data show that oligodendrocytes require MCL-1 to suppress apoptosis, implicate MCL-1 deficiency in white matter pathology, and suggest apoptosis inhibition as a leukodystrophy therapy.

Stress Relief Techniques: p38 MAPK Determines the Balance of Cell Cycle and Apoptosis Pathways

Protein signaling networks are formed from diverse and inter-connected cell signaling pathways converging into webs of function and regulation. These signaling pathways both receive and conduct molecular messages, often by a series of post-translation modifications such as phosphorylation or through protein-protein interactions via intrinsic motifs. The mitogen activated protein kinases (MAPKs) are components of kinase cascades that transmit signals through phosphorylation. There are several MAPK subfamilies, and one subfamily is the stress-activated protein kinases, which in mammals is the p38 family. The p38 enzymes mediate a variety of cellular outcomes including DNA repair, cell survival/cell fate decisions, and cell cycle arrest. The cell cycle is itself a signaling system that precisely controls DNA replication, chromosome segregation, and cellular division. Another indispensable cell function influenced by the p38 stress response is programmed cell death (apoptosis). As the regulators of cell survival, the BCL2 family of proteins and their dynamics are exquisitely sensitive to cell stress. The BCL2 family forms a protein-protein interaction network divided into anti-apoptotic and pro-apoptotic members, and the balance of binding between these two sides determines cell survival. Here, we discuss the intersections among the p38 MAPK, cell cycle, and apoptosis signaling pathways.

The multiple mechanisms of MCL1 in the regulation of cell fate

MCL1 (myeloid cell leukemia-1) is a widely recognized pro-survival member of the Bcl-2 (B-cell lymphoma protein 2) family and a promising target for cancer therapy. While the role MCL1 plays in apoptosis is well defined, its participation in emerging non-apoptotic signaling pathways is only beginning to be appreciated. Here, we synthesize studies characterizing MCL1s influence on cell proliferation, DNA damage response, autophagy, calcium handling, and mitochondrial quality control to highlight the broader scope that MCL1 plays in cellular homeostasis regulation. Throughout this review, we discuss which pathways are likely to be impacted by emerging MCL1 inhibitors, as well as highlight non-cancerous disease states that could deploy Bcl-2 homology 3 (BH3)-mimetics in the future.

In this review Widden and Placzek synthesize studies characterizing the influence that myeloid cell leukemia-1 (MCL1) has on cell proliferation, DNA damage response, autophagy, calcium handling, and mitochondrial quality control to highlight the broader scope that it plays in cellular homeostasis regulation. They discuss which pathways are likely to be impacted by emerging MCL1 inhibitors, as well as highlight non-cancerous disease states that could deploy BH3-mimetics in the future.

The Role of Mcl-1 in Embryonic Neural Precursor Cell Apoptosis

Myeloid cell leukemia-1 (Mcl-1), an anti-apoptotic Bcl-2 protein, regulates neural precursor cell (NPC) survival in both the developing and adult mammalian nervous system. It is unclear when during the neurogenic period Mcl-1 becomes necessary for NPC survival and whether Bax is the sole pro-apoptotic target of Mcl-1. To address these questions, we used the nervous system-specific Nestin-Cre Mcl-1 conditional knockout mouse line (Mcl-1 CKO) to assess the anti-apoptotic role of Mcl-1 in developmental neurogenesis. Loss of Mcl-1 resulted in a wave of apoptosis beginning in the brainstem and cervical spinal cord at embryonic day 9.5 (E9.5) and in the forebrain at E10.5. Apoptosis was first observed ventrally in each region and spread dorsally over time. Within the spinal cord, apoptosis also spread in a rostral to caudal direction following the path of differentiation. Breeding the Mcl-1 CKO mouse with the Bax null mouse rescued the majority of NPC from apoptosis except in the dorsomedial brainstem and ventral thoracic spinal cord where only 50% were rescued. This demonstrates that Mcl-1 promotes NPC survival primarily by inhibiting the activation of Bax, but that Bax is not the sole pro-apoptotic target of Mcl-1 during embryonic neurogenesis. Interestingly, although co-deletion of Bax rescued the majority of NPC apoptosis, it resulted in embryonic lethality at E13, whereas conditional deletion of both Mcl-1 and Bax rescued embryonic lethality. In summary, this study demonstrates the widespread dependency on Mcl-1 during nervous system development.

Targeting MCL-1 in hematologic malignancies: Rationale and progress

Myeloid cell leukemia sequence 1 (MCL-1) is an antiapoptotic protein that plays a key role in promoting cell survival in multiple myeloma (MM), acute myeloid leukemia (AML), and non-Hodgkin lymphoma (NHL). Overexpression of MCL-1 is associated with treatment resistance and poor prognosis; thus, MCL-1 inhibitors are rational therapeutic options for malignancies depending on MCL-1. Several MCL-1 inhibitors have entered clinical trials, including AZD5991, S64315, AMG 176, and AMG 397. A key area of investigation is whether MCL-1 inhibitors will complement the activity of BCL-2 inhibitors, such as venetoclax, and synergistically enhance anti-tumor efficacy when given in combination with other anti-cancer drugs. Another important question is whether a safe therapeutic window can be found for this new class of inhibitors. In summary, inhibition of MCL-1 shows potential as a treatment for hematologic malignancies and clinical evaluation of MCL-1 inhibitors is currently underway.

Mcl1 protein levels and Caspase-7 executioner protease control axial organizer cells survival

BACKGROUND

Organizing centers are groups of specialized cells that secrete morphogens, thereby influencing development of their neighboring territories. Apoptosis is a form of programmed cell death reported to limit the size of organizers. Little is known about the identity of intracellular signals driving organizer cell death. Here we investigated in Xenopus the role of both the anti-apoptotic protein Myeloid-cell-leukemia 1 (Mcl1) and the cysteine proteases Caspase-3 and Caspase-7 in formation of the axial organizing center-the notochord-that derives from the Spemann organizer, and participates in the induction and patterning of the neuroepithelium.

RESULTS

We confirm a role for apoptosis in establishing the axial organizer in early neurula. We show that the expression pattern of mcl1 is coherent with a role for this gene in early notochord development. Using loss of function approaches, we demonstrate that Mcl1 depletion decreases neuroepithelium width and increases notochord cells apoptosis, a process that relies on Caspase-7, and not on Caspase-3, activity. Our data provide evidence that Mcl1 protein levels physiologically control notochord cells' survival and that Caspase-7 is the executioner protease in this developmental process.

CONCLUSIONS

Our study reveals new functions for Mcl1 and Caspase-7 in formation of the axial signalling center.

MCL1 binding to the reverse BH3 motif of P18INK4C couples cell survival to cell proliferation

Commitment to cell cycle entry and cellular duplication is a tightly coordinated and regulated process. Once initiated, a series of multiple checkpoints ensure both accurate genomic replication and chromosomal separation. In the event of unsuccessful cell division, parallel pathways exist that induce the cell to undergo programmed cell death, or apoptosis. At the center of such stress-induced, intrinsic apoptotic regulation lies the BCL2 family of pro- and anti-apoptotic regulatory proteins. In a proliferative state the balance of pro- and anti-apoptotic signaling proteins would be expected to favor an excess population of anti-apoptotic members. While the anti-apoptotic BCL2 family member, MCL1, has been identified to oversee mitotic progression, direct communication between the BCL2 family and cell proliferation has not been observed. In this study, we demonstrate a direct protein–protein interaction between MCL1 and the G₁/S checkpoint protein, P18INK4C. This interaction is mediated by a reverse BH3 (rBH3) motif located in P18INK4C’s C-terminal ankyrin repeat. MCL1 is further shown to decrease P18INK4C expression and thereby regulate cell cycle entry in a retinoblastoma (RB1)-dependent manner. Our findings establish a mechanism for translation independent and direct communication between the BCL2 family regulation of apoptosis and CDK4/6-RB regulation of early G₁/S transition during cellular division/growth.

Bcl-2 family proteins, beyond the veil

Apoptosis is an important part of both health and disease and is often regulated by the BCL-2 family of proteins. These proteins are either pro- or anti-apoptotic, existing in a delicate balance during homeostasis. They are best known for their role in regulating the activation of caspases and the execution of a cell in response to a variety of stimuli. However, it is often forgotten that these BCL-2 family proteins also have important roles to play in cell maintenance that are not associated with apoptosis. These include roles in regulating processes such as cell cycle progression, mitochondrial function, autophagy, intracellular calcium concentration, glucose and lipid metabolism, and the unfolded protein response. In addition to these established alternate functions, further discoveries are being made that have potential therapeutic benefits in diseases such as cancer. BOK, a BCL-2 family protein thought comparable to multidomain pro-apoptotic proteins BAX and BAK, has recently been identified as a key player in metabolism of and resistance to the commonly used chemotherapeutic 5-FU. As a result of such findings, which could see the potential use of BOK as a biomarker for 5-FU sensitivity or mimetic molecules as a resensitization strategy, new targets and mechanisms of pathology may arise from further investigation into the realm of alternate functions of BCL-2 family proteins.

Divide or Commit - Revisiting the Role of Cell Cycle Regulators in Adult Hippocampal Neurogenesis

The adult dentate gyrus continuously generates new neurons that endow the brain with increased plasticity, helping to cope with changing environmental and cognitive demands. The process leading to the birth of new neurons spans several precursor stages and is the result of a coordinated series of fate decisions, which are tightly controlled by extrinsic signals. Many of these signals act through modulation of cell cycle (CC) components, not only to drive proliferation, but also for linage commitment and differentiation. In this review, we provide a comprehensive overview on key CC components and regulators, with emphasis on G₁ phase, and analyze their specific functions in precursor cells of the adult hippocampus. We explore their role for balancing quiescence versus self-renewal, which is essential to maintain a lifelong pool of neural stem cells while producing new neurons “on demand.” Finally, we discuss available evidence and controversies on the impact of CC/G₁ length on proliferation versus differentiation decisions.

Mcl-1 and Bcl-xL are essential for survival of the developing nervous system

During neurogenesis, proliferating neural precursor cells (NPC) exit the cell cycle and differentiate into postmitotic neurons. The proteins that regulate cell survival through the stages of differentiation, however, are still poorly understood. Here, we examined the roles of the anti-apoptotic Bcl-2 proteins, Mcl-1 and Bcl-xL, in promoting survival as cells progress through the stages of neurogenesis in the mouse embryonic central nervous system. We used Nestin-mediated, nervous system-specific conditional deletion of mcl-1, bcl-x or both to identify their distinct and overlapping roles. Individual conditional deletion of mcl-1 (MKO) and bcl-x (BKO) suggested sequential roles in promoting cell survival during developmental neurogenesis. In the MKO embryo, apoptosis begins at embryonic day 10 (E10) in the proliferating NPC population throughout the entire developing nervous system. In the BKO embryo, apoptosis begins later at E11 within the postmitotic neuron populations. In the double (mcl-1 and bcl-x) conditional knockout (DKO), cell death extended throughout both proliferating and non-proliferating cell populations resulting in embryonic lethality at E12, earlier than in either the MKO or BKO. Apoptotic cell death of the entire central nervous system in the DKO demonstrates that both genes are necessary for cell survival during developmental neurogenesis. To determine whether Mcl-1 and Bcl-xL have overlapping anti-apoptotic roles during neurogenesis, we examined the impact of gene dosage. Loss of a single bcl-x allele in the MKO embryo exasperated apoptotic cell death within the NPC population revealing a novel anti-apoptotic role for Bcl-xL in proliferating NPCs. Cells were rescued from apoptosis in both the MKO and BKO embryos by breeding with the Bax null mouse line indicating that Mcl-1 and Bcl-xL have a common pro-apoptotic target during developmental neurogenesis. Taken together, these findings demonstrate that Mcl-1 and Bcl-xL are the two essential anti-apoptotic Bcl-2 proteins required for the survival of the developing mammalian nervous system.

Intrinsic apoptotic pathway activation increases response to anti-estrogens in luminal breast cancers

Estrogen receptor-α positive (ERα+) breast cancer accounts for approximately 70–80% of the nearly 25,0000 new cases of breast cancer diagnosed in the US each year. Endocrine-targeted therapies (those that block ERα activity) serve as the first line of treatment in most cases. Despite the proven benefit of endocrine therapies, however, ERα+ breast tumors can develop resistance to endocrine therapy, causing disease progression or relapse, particularly in the metastatic setting. Anti-apoptotic Bcl-2 family proteins enhance breast tumor cell survival, often promoting resistance to targeted therapies, including endocrine therapies. Herein, we investigated whether blockade of anti-apoptotic Bcl-2 family proteins could sensitize luminal breast cancers to anti-estrogen treatment. We used long-term estrogen deprivation (LTED) of human ERα+ breast cancer cell lines, an established model of sustained treatment with and acquired resistance to aromatase inhibitors (AIs), in combination with Bcl-2/Bcl-xL inhibition (ABT-263), finding that ABT-263 induced only limited tumor cell killing in LTED-selected cells in culture and in vivo. Interestingly, expression and activity of the Bcl-2-related factor Mcl-1 was increased in LTED cells. Genetic Mcl-1 ablation induced apoptosis in LTED-selected cells, and potently increased their sensitivity to ABT-263. Increased expression and activity of Mcl-1 was similarly seen in clinical breast tumor specimens treated with AI + the selective estrogen receptor downregulator fulvestrant. Delivery of Mcl-1 siRNA loaded into polymeric nanoparticles (MCL1 si-NPs) decreased Mcl-1 expression in LTED-selected and fulvestrant-treated cells, increasing tumor cell death and blocking tumor cell growth. These findings suggest that Mcl-1 upregulation in response to anti-estrogen treatment enhances tumor cell survival, decreasing response to therapeutic treatments. Therefore, strategies blocking Mcl-1 expression or activity used in combination with endocrine therapies would enhance tumor cell death.

Myeloid cell leukemia 1 (MCL-1), an unexpected modulator of protein kinase signaling during invasion

Myeloid cell leukemia-1 (MCL-1), closely related to B-cell lymphoma 2 (BCL-2), has a well-established role in cell survival and has emerged as an important target for cancer therapeutics. We have demonstrated that inhibiting MCL-1 is efficacious in suppressing tumour progression in pre-clinical models of breast cancer and revealed that in addition to its role in cell survival, MCL-1 modulated cellular invasion. Utilizing a MCL-1-specific genetic antagonist, we found two possible mechanisms; firstly MCL-1 directly binds to and alters the phosphorylation of the cytoskeletal remodeling protein, Cofilin, a protein important for cytoskeletal remodeling during invasion, and secondly MCL-1 modulates the levels SRC family kinases (SFKs) and their targets. These data provide evidence that MCL-1 activities are not limited to endpoints of extracellular and intracellular signaling culminating in cell survival as previously thought, but can directly modulate the output of SRC family kinases signaling during cellular invasion. Here we review the pleotropic roles of MCL-1 and discuss the implications of this newly discovered effect on protein kinase signaling for the development of cancer therapeutics.

Disruptions in asymmetric centrosome inheritance and WDR62-Aurora kinase B interactions in primary microcephaly

Recessive mutations in WD repeat domain 62 (WDR62) cause microcephaly and a wide spectrum of severe brain malformations. Disruption of the mouse ortholog results in microcephaly underlain by reduced proliferation of neocortical progenitors during late neurogenesis, abnormalities in asymmetric centrosome inheritance leading to neuronal migration delays, and altered neuronal differentiation. Spindle pole localization of WDR62 and mitotic progression are defective in patient-derived fibroblasts, which, similar to mouse neocortical progenitors, transiently arrest at prometaphase. Expression of WDR62 is closely correlated with components of the chromosome passenger complex (CPC), a key regulator of mitosis. Wild type WDR62, but not disease-associated mutant forms, interacts with the CPC core enzyme Aurora kinase B and staining of CPC components at centromeres is altered in patient-derived fibroblasts. Our findings demonstrate critical and diverse functions of WDR62 in neocortical development and provide insight into the mechanisms by which its disruption leads to a plethora of structural abnormalities.

Bcl-xL dependency coincides with the onset of neurogenesis in the developing mammalian spinal cord

The bcl-2 family of survival and death promoting proteins play a key role in regulating cell numbers during nervous system development. Bcl-x_L, an anti-apoptotic bcl-2 family member is highly expressed in the developing nervous system. However; the early embryonic lethality of the bcl-x germline null mouse precluded an investigation into its role in nervous system development. To identify the role of bcl-x in spinal cord neurogenesis, we generated a central nervous system-specific bcl-x conditional knockout (BKO) mouse. Apoptotic cell death in the BKO embryo was initially detected at embryonic day 11 (E11) in the ventrolateral aspect of the spinal cord corresponding to the location of motor neurons. Apoptosis reached its peak at E13 having spread across the ventral and into the dorsal spinal cord. By E18, the wave of apoptosis had passed and only a few apoptotic cells were observed. The duration and direction of spread of apoptosis across the spinal cord is consistent with the spatial and temporal sequence of neuronal differentiation. Motor neurons, the first neurons to become post mitotic in the spinal cord, were also the first apoptotic cells. As neurogenesis spread across the spinal cord, later born neuronal populations such as Lim2⁺ interneurons were also affected. The onset of apoptosis occurred in cells that had exited the cell cycle within the previous 24h and initiated neural differentiation as demonstrated by BrdU birthdating and βIII tubulin immunohistochemistry. This data demonstrates that spinal cord neurons become Bcl-x_L dependent at an early post mitotic stage in developmental neurogenesis.

RHEB: a potential regulator of chondrocyte phenotype for cartilage tissue regeneration

As articular cartilage has a limited ability to self-repair, successful cartilage regeneration requires clinical-grade chondrocytes with innate characteristics. However, cartilage regeneration via chondrocyte transplantation is challenging, because chondrocytes lose their innate characteristics during in vitro expansion. Here, we investigated the mechanistic underpinning of the gene Ras homologue enriched in brain (RHEB) in the control of senescence and dedifferentiation through the modulation of oxidative stress in chondrocytes, a hallmark of osteoarthritis. Serial expansion of human chondrocytes led to senescence, dedifferentiation and oxidative stress. RHEB maintained the innate characteristics of chondrocytes by regulating senescence, dedifferentiation and oxidative stress, leading to the upregulation of COL2 expression via SOX9 and the downregulation of p27 expression via MCL1. RHEB also decreased the expression of COL10. RHEB knockdown mimics decreased the expression of SOX9, COL2 and MCL1, while abrogating the suppressive function of RHEB on p27 and COL10 in chondrocytes. RHEB-overexpressing chondrocytes successfully formed cartilage tissue in vitro as well as in vivo, with increased expression of GAG matrix and chondrogenic markers. RHEB induces a distinct gene expression signature that maintained the innate chondrogenic properties over a long period. Therefore, RHEB expression represents a potentially useful mechanism in terms of cartilage tissue regeneration from chondrocytes, by which chondrocyte phenotypic and molecular characteristics can be retained through the modulation of senescence, dedifferentiation and oxidative stress. Copyright © 2016 John Wiley & Sons, Ltd.

Mechanistic rationale for MCL1 inhibition during androgen deprivation therapy

Androgen deprivation therapy induces apoptosis or cell cycle arrest in prostate cancer (PCa) cells. Here we set out to analyze whether MCL1, a known mediator of chemotherapy resistance regulates the cellular response to androgen withdrawal. Analysis of MCL1 protein and mRNA expression in PCa tissue and primary cell culture specimens of luminal and basal origin, respectively, reveals higher expression in cancerous tissue compared to benign origin. Using PCa cellular models in vitro and in vivo we show that MCL1 expression is upregulated in androgen-deprived PCa cells. Regulation of MCL1 through the AR signaling axis is indirectly mediated via a cell cycle-dependent mechanism. Using constructs downregulating or overexpressing MCL1 we demonstrate that expression of MCL1 prevents induction of apoptosis when PCa cells are grown under steroid-deprived conditions. The BH3-mimetic Obatoclax induces apoptosis and decreases MCL1 expression in androgen-sensitive PCa cells, while castration-resistant PCa cells are less sensitive and react with an upregulation of MCL1 expression. Synergistic effects of Obatoclax with androgen receptor inactivation can be observed. Moreover, clonogenicity of primary basal PCa cells is efficiently inhibited by Obatoclax. Altogether, our results suggest that MCL1 is a key molecule deciding over the fate of PCa cells upon inactivation of androgen receptor signaling.

GRM7 regulates embryonic neurogenesis via CREB and YAP

Metabotropic glutamate receptor 7 (GRM7) has recently been identified to be associated with brain developmental defects, such as attention deficit hyperactivity disorder (ADHD) and autism. However, the function of GRM7 during brain development remains largely unknown. Here, we used gain- and loss-of-function strategies to investigate the role of GRM7 in early cortical development. We demonstrate that Grm7 knockdown increases neural progenitor cell (NPC) proliferation, decreases terminal mitosis and neuronal differentiation, and leads to abnormal neuronal morphology. GRM7 regulates the phosphorylation of cyclic AMP response element-binding protein (CREB) and the expression of Yes-associated protein (YAP) by directly interacting with CaM, which subsequently regulates the expression of CyclinD1 and ultimately affects early cortical development. These defects in neurogenesis are ameliorated by Grm7 overexpression, Creb knockdown, or Yap knockdown. Thus, our findings indicate that GRM7 signaling via CREB and YAP is necessary for neurogenesis in the brain.

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GRM7 is essential for brain development and neuron production

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GRM7 acts through CREB and YAP to regulate neurogenesis

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Grm7 knockdown causes neuronal development defects

aPKC phosphorylates p27Xic1, providing a mechanistic link between apicobasal polarity and cell-cycle control

During the development of the nervous system, apicobasally polarized stem cells are characterized by a shorter cell cycle than nonpolar progenitors, leading to a lower differentiation potential of these cells. However, how polarization might be directly linked to the kinetics of the cell cycle is not understood. Here, we report that apicobasally polarized neuroepithelial cells in Xenopus laevis have a shorter cell cycle than nonpolar progenitors, consistent with mammalian systems. We show that the apically localized serine/threonine kinase aPKC directly phosphorylates an N-terminal site of the cell-cycle inhibitor p27Xic1 and reduces its ability to inhibit the cyclin-dependent kinase 2 (Cdk2), leading to shortening of G1 and S phases. Overexpression of activated aPKC blocks the neuronal differentiation-promoting activity of p27Xic1. These findings provide a direct mechanistic link between apicobasal polarity and the cell cycle, which may explain how proliferation is favored over differentiation in polarized neural stem cells.

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aPKC shortens G1 and S phases of cell cycle by phosphorylating p27Xic1

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Phosphorylated p27Xic1 exhibits weaker binding to and inhibition of Cdk2

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p27Xic1 promotes neuronal differentiation and elongates cell cycle via G1 phase

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Effects of p27Xic1 on neuronal differentiation are rescued by activated aPKC

Early development of the neural plate: new roles for apoptosis and for one of its main effectors caspase-3

Despite its tremendous complexity, the vertebrate nervous system emerges from a homogenous layer of neuroepithelial cells, the neural plate. Its formation relies on the time- and space-controlled progression of developmental programs. Apoptosis is a biological process that removes superfluous and potentially dangerous cells and is implemented through the activation of a molecular pathway conserved during evolution. Apoptosis and an unconventional function of one of its main effectors, caspase-3, contribute to the patterning and growth of the neuroepithelium. Little is known about the intrinsic and extrinsic cues controlling activities of the apoptotic machinery during development. The BarH-like (Barhl) proteins are homeodomain-containing transcription factors. The observations in Caenorhabditis elegans, Xenopus, and mice document that Barhl proteins act in cell survival and as cell type-specific regulators of a caspase-3 function that limits neural progenitor proliferation. In this review, we discuss the roles and regulatory modes of the apoptotic machinery in the development of the neural plate. We focus on the Barhl2, the Sonic Hedgehog, and the Wnt pathways and their activities in neural progenitor survival and proliferation.

Revisiting the role of MCL1 in tumorigenesis of solid cancer: gene expression correlates with antiproliferative phenotype in breast cancer cells and its functional regulatory variants are associated with reduced cancer susceptibility

Compared to the well-defined anti-apoptotic role of myeloid cell leukemia sequence 1 (MCL1), its antiproliferative function in tumorigenesis is less studied. We had recently reported that regulatory variants of MCL1 contribute to enhanced promoter activity but reduced risk of lung cancer. We hypothesized that MCL1 expression may manifest antiproliferative phenotype and its functional variations may have etiological relevance for breast cancer. We manipulated MCL1 expression in MCF-7 cells and MDA231 with overexpression and knockdown, analyzed the effects on cell viability and cell cycling phase, and characterized the correlation with expression profiles of key regulators of cell cycle. We further genotyped the -190 insertion polymorphism and the neighboring single nucleotide polymorphisms (SNPs) in 745 breast cancer patients and 537 controls and analyzed their association with cancer risk. We confirmed that heightened expression of MCL1 resulted in decreased proliferation ability of breast cancer cells. We further observed that MCL1 overexpression in breast cancer cells resulted in cell cycle progression arresting in S phase and concomitant enhanced expression of p27, which could be rescued by p27 knockdown with co-transfection of small interfering RNA (siRNA). Furthermore, we found a significant reduction in breast cancer risk [odds ratio (OR) = 0.74; 95 % confidence interval (CI) = 0.59-0.93] associated with -190 insertion genotype; the expression-enhancing regulatory haplotype (OR 0.79; 95 % CI 0.66-0.95) and diplotype (OR 0.71; 95 % CI 0.57-0.89) were consistently associated with decreased cancer susceptibility. The study demonstrates that the expression-enhancing regulatory variants of MCL1 are protective modifiers of breast cancer risk, and reduced cell proliferation and arrested cell cycle progression partly mediated by p27 might be the underlying mechanism.