Loss of AMPKalpha1 Triggers Centrosome Amplification via PLK4 Upregulation in Mouse Embryonic Fibroblasts.

Recent evidence indicates that activation of adenosine monophosphate-activated protein kinase (AMPK), a highly conserved sensor and modulator of cellular energy and redox, regulates cell mitosis. However, the underlying molecular mechanisms for AMPKα subunit regulation of chromosome segregation remain poorly understood. This study aimed to ascertain if AMPKα1 deletion contributes to chromosome missegregation by elevating Polo-like kinase 4 (PLK4) expression. Centrosome proteins and aneuploidy were monitored in cultured mouse embryonic fibroblasts (MEFs) isolated from wild type (WT, C57BL/6J) or AMPKα1 homozygous deficient (AMPKα1-/-) mice by Western blotting and metaphase chromosome spread. Deletion of AMPKα1, the predominant AMPKα isoform in immortalized MEFs, led to centrosome amplification and chromosome missegregation, as well as the consequent aneuploidy (34-66%) and micronucleus. Furthermore, AMPKα1 null cells exhibited a significant induction of PLK4. Knockdown of nuclear factor kappa B2/p52 ameliorated the PLK4 elevation in AMPKα1-deleted MEFs. Finally, PLK4 inhibition by Centrinone reversed centrosome amplification of AMPKα1-deleted MEFs. Taken together, our results suggest that AMPKα1 plays a fundamental role in the maintenance of chromosomal integrity through the control of p52-mediated transcription of PLK4, a trigger of centriole biogenesis.

Gefitinib-mediated reactive oxygen specie (ROS) instigates mitochondrial dysfunction and drug resistance in lung cancer cells.

Therapeutic benefits offered by tyrosine kinase inhibitors (TKIs), such as gefitinib (Iressa) and erlotinib (Tarceva), are limited due to the development of resistance, which contributes to treatment failure and cancer-related mortality. The aim of this study was to elucidate mechanistic insight into cellular perturbations that accompany acquired gefitinib resistance in lung cancer cells. Several lung adenocarcinoma (LAD) cell lines were screened to characterize epidermal growth factor receptor (EGFR) expression and mutation profile. To circumvent intrinsic variations between cell lines with respect to response to drug treatments, we generated gefitinib-resistant H1650 clone by long-term, chronic culture under gefitinib selection of parental cell line. Isogenic cells were analyzed by microarray, Western blot, flow cytometry, and confocal and transmission electron microscope. We observed that although chronic gefitinib treatment provided effective action against its primary target (aberrant EGFR activity), secondary effects resulted in increased cellular reactive oxygen species (ROS). Gefitinib-mediated ROS correlated with epithelial-mesenchymal transition, as well as striking perturbation of mitochondrial morphology and function. However, gefitinib treatment in the presence of ROS scavenger provided a partial rescue of mitochondrial aberrations. Furthermore, withdrawal of gefitinib from previously resistant clones correlated with normalized expression of epithelial-mesenchymal transition genes. These findings demonstrate that chronic gefitinib treatment promotes ROS and mitochondrial dysfunction in lung cancer cells. Antioxidants may alleviate ROS-mediated resistance.

AMPKα1 deficiency promotes cellular proliferation and DNA damage via p21 reduction in mouse embryonic fibroblasts.

Emerging evidence suggests that activation of adenosine monophosphate-activated protein kinase (AMPK), an energy gauge and redox sensor, controls the cell cycle and protects against DNA damage. However, the molecular mechanisms by which AMPKα isoform regulates DNA damage remain largely unknown. The aim of this study was to determine if AMPKα deletion contributes to cellular hyperproliferation by reducing p21(WAF1/Cip1) (p21) expression thereby leading to accumulated DNA damage. The markers for DNA damage, cell cycle proteins, and apoptosis were monitored in cultured mouse embryonic fibroblasts (MEFs) isolated from wild type (WT, C57BL/6J), AMPKα1, or AMPKα2 homozygous deficient (AMPKα1(-/-), AMPKα2(-/-)) mice by Western blot, flow cytometry, and cellular immunofluorescence staining. Deletion of AMPKα1, the predominant AMPKα isoform, but not AMPKα2 in immortalized MEFs led to spontaneous DNA double-strand breaks (DSB) which corresponded to repair protein p53-binding protein 1 (53BP1) foci formation and subsequent apoptosis. Furthermore, AMPKα1 localizes to chromatin and AMPKα1 deletion down-regulates cyclin-dependent kinase inhibitor, p21, an important protein that plays a role in decreasing the incidence of spontaneous DSB via inhibition of cell proliferation. In addition, AMPKα1 null cells exhibited enhanced cell proliferation. Finally, p21 overexpression partially blocked the cellular hyperproliferation of AMPKα1-deleted MEFs via the inhibition of cyclin-dependent kinase 2 (CDK2). Taken together, our results suggest that AMPKα1 plays a fundamental role in controlling the cell cycle thereby affecting DNA damage and cellular apoptosis.

Liver kinase B1 expression promotes phosphatase activity and abrogation of receptor tyrosine kinase phosphorylation in human cancer cells.

Aberrant receptor tyrosine kinase phosphorylation (pRTK) has been associated with diverse pathological conditions, including human neoplasms. In lung cancer, frequent liver kinase B1 (LKB1) mutations correlate with tumor progression, but potential links with pRTK remain unknown. Heightened and sustained receptor activation was demonstrated by LKB1-deficient A549 (lung) and HeLaS3 (cervical) cancer cell lines. Depletion (siRNA) of endogenous LKB1 expression in H1792 lung cancer cells also correlated with increased pRTK. However, ectopic LKB1 expression in A549 and HeLaS3 cell lines, as well as H1975 activating-EGF receptor mutant lung cancer cell resulted in dephosphorylation of several tumor-enhancing RTKs, including EGF receptor, ErbB2, hepatocyte growth factor receptor (c-Met), EphA2, rearranged during transfection (RET), and insulin-like growth factor I receptor. Receptor abrogation correlated with attenuation of phospho-Akt and increased apoptosis. Global phosphatase inhibition by orthovanadate or depletion of protein tyrosine phosphatases (PTPs) resulted in the recovery of receptor phosphorylation. Specifically, the activity of SHP-2, PTP-1ß, and PTP-PEST was enhanced by LKB1-expressing cells. Our findings provide novel insight on how LKB1 loss of expression or function promotes aberrant RTK signaling and rapid growth of cancer cells.

Adenosine monophosphate-activated protein kinase-α2 deficiency promotes vascular smooth muscle cell migration via S-phase kinase-associated protein 2 upregulation and E-cadherin downregulation.

OBJECTIVE: Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are critical events in the progression of several vasculopathologies. Adenosine monophosphate-activated protein kinase (AMPK) has been shown to play a pivotal role in cellular proliferation and migration. However, the roles of AMPK in VSMC migration and its underlying molecular mechanisms remain elusive. APPROACH AND RESULTS: VSMC migration and the neointima formation were studied in cultured mouse VSMCs or in carotid artery ligation of wild-type C57BL/6J mice, AMPKα2, AMPKα1 homozygous-deficient (AMPKα2(-/-), AMPKα1(-/-)) mice. Deletion of AMPKα2, but not AMPKα1, led to increased phosphorylation of both IкB kinase α and its downstream target nuclear factor кB2/p100 at serine 866/870. Consequently, phosphor-p100 at S866/870 bound with E3 ubiquitin ligase ß-transducin repeat-containing protein resulting in the proteolytic processing of the p100 precursor and nuclear factor кB2/p52 induction. Interestingly, acetylation of histone H3 at lysine 56 mediated by histone deacetylase-3 reduction was enhanced significantly in AMPKα2(-/-) VSMCs compared with wild-type or AMPKα1(-/-) VSMCs. Moreover, the augmented association of p52/acetylation of histone H3 at lysine 56 with the promoter of ubiquitin E3 ligase, S-phase kinase-associated protein 2, was shown in AMPKα2(-/-) VSMCs by chromatin immunoprecipitation assay. Furthermore, AMPKα2 deletion caused S-phase kinase-associated protein 2-mediated E-cadherin downregulation. S-Phase kinase-associated protein 2 siRNA abolished the increased migration of AMPKα2(-/-) VSMCs via E-cadherin upregulation. Finally, neointima formation after ligation of carotid artery was increased in AMPKα2(-/-), but not AMPKα1(-/-), mice. CONCLUSIONS: We conclude that deletion of AMPKα2 causes aberrant VSMC migration with accelerated neointima formation in vivo.

The yin-yang of DNA damage response: roles in tumorigenesis and cellular senescence.

Senescent cells are relatively stable, lacking proliferation capacity yet retaining metabolic activity. In contrast, cancer cells are rather invasive and devastating, with uncontrolled proliferative capacity and resistance to cell death signals. Although tumorigenesis and cellular senescence are seemingly opposite pathological events, they are actually driven by a unified mechanism: DNA damage. Integrity of the DNA damage response (DDR) network can impose a tumorigenesis barrier by navigating abnormal cells to cellular senescence. Compromise of DDR, possibly due to the inactivation of DDR components, may prevent cellular senescence but at the expense of tumor formation. Here we provide an overview of the fundamental role of DDR in tumorigenesis and cellular senescence, under the light of the Yin-Yang concept of Chinese philosophy. Emphasis is placed on discussing DDR outcome in the light of in vivo models. This information is critical as it can help make better decisions for clinical treatments of cancer patients.

Aberrant NRP-1 expression serves as predicator of metastatic endometrial and lung cancers.

Neuropilin-1 (NRP-1) has emerged as an important driver of tumor-promoting phenotypes of human malignancies. However, incomplete knowledge exists as to how this single-pass transmembrane receptor mediates pleiotropic tumor-promoting functions. The purpose of this study was to evaluate NRP-1 expression and metastatic properties in 94 endometrial cancer and matching serum specimens and in a lung cancer cell line. We found that NRP-1 expression significantly correlated with increased tumoral expression of vascular endothelial growth factor 2 (VEGFR2) and serum levels of hepatocyte growth factor (HGF) and cell growth-stimulating factor (C-GSF). Tumoral NRP-1 also was positively associated with expression of NEDD9, a pro-metastatic protein. In the highly metastatic lung cancer cell line (H1792), stable LKB1 depletion caused increased migration in vitro and accentuated NRP-1 and NEDD9 expression in vivo. Our findings demonstrate that perturbed expression of these targets correlate with metastatic potential of endometrial and lung tumors, providing clinically-relevant biomarker applications for diagnostic and therapeutic targeting.

Protein kinase LKB1 promotes RAB7-mediated neuropilin-1 degradation to inhibit angiogenesis.

After internalization, transmembrane receptors (TMRs) are typically recycled back to the cell surface or targeted for degradation. Efficient TMR trafficking is critical for regulation of several processes, including signal transduction pathways, development, and disease. Here, we determined that trafficking of the angiogenic receptor neuropilin-1 (NRP-1) is abrogated by the liver kinase B1 (LKB1), a serine-threonine kinase of the calcium calmodulin family. We found that aberrant NRP-1 expression in tumor cells from patients with lung adenocarcinoma is associated with decreased levels of LKB1. In cultured lung cells, LKB1 accentuated formation of a complex between NRP-1 and RAB7 in late endosomes. LKB1 specifically bound GTP-bound RAB7, but not a dominant-negative GDP-bound form of RAB7, promoting rapid transfer and lysosome degradation of NRP-1. siRNA-mediated depletion of RAB7 disrupted the transfer of NRP-1 to the lysosome, resulting in recovery of the receptor as well as increased tumor growth and angiogenesis. Together, our findings indicate that LKB1 functions as a RAB7 effector and suppresses angiogenesis by promoting the cellular trafficking of NRP-1 from RAB7 vesicles to the lysosome for degradation. Furthermore, these data suggest that LKB1 and NRP-1 have potential as therapeutic targets for limiting tumorigenesis.