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Involvement of maternal embryonic leucine zipper kinase (MELK) in mammary carcinogenesis through interaction with Bcl-G, a pro-apoptotic member of the Bcl-2 family.

ABSTRACT: INTRODUCTION: Cancer therapies directed at specific molecular targets in signaling pathways of cancer cells, such as tamoxifen, aromatase inhibitors and trastuzumab, have proven useful for treatment of advanced breast cancers. However, increased risk of endometrial cancer with long-term tamoxifen administration and of bone fracture due to osteoporosis in postmenopausal women undergoing aromatase inhibitor therapy are recognized side effects. These side effects as well as drug resistance make it necessary to search for novel molecular targets for drugs on the basis of well-characterized mechanisms of action. METHODS: Using accurate genome-wide expression profiles of breast cancers, we found maternal embryonic leucine-zipper kinase (MELK) to be significantly overexpressed in the great majority of breast cancer cells. To assess whether MELK has a role in mammary carcinogenesis, we knocked down the expression of endogenous MELK in breast cancer cell lines using mammalian vector-based RNA interference. Furthermore, we identified a long isoform of Bcl-G (Bcl-GL), a pro-apoptotic member of the Bcl-2 family, as a possible substrate for MELK by pull-down assay with recombinant wild-type and kinase-dead MELK. Finally, we performed TUNEL assays and FACS analysis, measuring proportions of apoptotic cells, to investigate whether MELK is involved in the apoptosis cascade through the Bcl-GL-related pathway. RESULTS: Northern blot analyses on multiple human tissues and cancer cell lines demonstrated that MELK was overexpressed at a significantly high level in a great majority of breast cancers and cell lines, but was not expressed in normal vital organs (heart, liver, lung and kidney). Suppression of MELK expression by small interfering RNA significantly inhibited growth of human breast cancer cells. We also found that MELK physically interacted with Bcl-GL through its amino-terminal region. Immunocomplex kinase assay showed that Bcl-GL was specifically phosphorylated by MELK in vitro. TUNEL assays and FACS analysis revealed that overexpression of wild-type MELK suppressed Bcl-GL-induced apoptosis, while that of D150A-MELK did not. CONCLUSION: Our findings suggest that the kinase activity of MELK is likely to affect mammary carcinogenesis through inhibition of the pro-apoptotic function of Bcl-GL. The kinase activity of MELK could be a promising molecular target for development of therapy for patients with breast cancers.

SUBMITTER: Lin ML

PROVIDER: S-EPMC1851384 | biostudies-literature | 2007

REPOSITORIES: biostudies-literature

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Involvement of maternal embryonic leucine zipper kinase (MELK) in mammary carcinogenesis through interaction with Bcl-G, a pro-apoptotic member of the Bcl-2 family.

Lin Meng-Lay ML Park Jae-Hyun JH Nishidate Toshihiko T Nakamura Yusuke Y Katagiri Toyomasa T

Breast cancer research : BCR 20070101 1

<h4>Introduction</h4>Cancer therapies directed at specific molecular targets in signaling pathways of cancer cells, such as tamoxifen, aromatase inhibitors and trastuzumab, have proven useful for treatment of advanced breast cancers. However, increased risk of endometrial cancer with long-term tamoxifen administration and of bone fracture due to osteoporosis in postmenopausal women undergoing aromatase inhibitor therapy are recognized side effects. These side effects as well as drug resistance m ...[more]

PMID: 17280616

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Project description:Purpose: Gene expression analyses comparing tumors of different behaviors have been used for the identification of genes that have a role in the growth and maintenance of tumors, with the aim of both understanding the molecular basis of tumorigenesis and identifying novel potential therapeutic targets. We have here used this approach to identify the underlying gene expression differences between highly invasive glioblastoma multiforme and typically benign pilocytic astrocytomas. Experimental Design: We performed cDNA microarray analyses comparing astrocytomas of polar grade: grade I, pilocytic astrocytoma (PA), the non-invasive and most frequent pediatric tumor, with grade IV, the highly infiltrative glioblastoma multiforme (GBM) Results: Despite the significant clinical and pathological differences between the two tumor types, only 63 genes were found to exhibit two-fold or greater over-expression in GBM as compared with PA. A functional classification of the GBM over-expressed genes indicated that more than 50% are related to the regulation of the cell cycle and mitosis. Microarray data was validated by RQ-PCR testing six over-expressed genes in GBM related to PA: MELK, AUKB, ASPM, PRC1, IL13RA2 and KIAA0101. The differential expression was confirmed for all six genes, showing at least a 5 fold increase in the average expression levels in GBM compared to PA. Of the over expressed genes, that which exhibited the most statistically significant difference is Maternal Embryonic Leucine zipper Kinase (MELK). We undertook a more detailed investigation of the expression of this serine/threonine kinase gene in astrocytomas in the light of its role in the regulation of multipotent neural progenitor proliferation and previous suggestions that this may be a oncogenic target of general importance. In an examination of more than 100 tumors of the central nervous system we found progressively higher expression of MELK in GBM with astrocytoma grade and a noteworthy uniformity of high level expression in GBM. This latter feature probably explains the lack of observed association of MELK expression with survival of GBM patients. Over-expression at a similar level to GBM was also observed in medulloblastoma. We found neither gene methylation nor amplification to be a factor in MELK expression but were able to demonstrate that MELK knockdown in malignant astrocytoma cell lines caused a reduction in proliferation and anchorage-independent growth in in vitro assays. Conclusions: Our results indicate that GBM and PA differ by the expression of surprisingly few genes. Among them, MELK may play a key role in differentiating these two tumor types and represent an important therapeutic target for the management of the most frequent brain tumors in adult and children. Keywords: Comparizon of CNS tumors of different grades.

Dataset Information

Involvement of maternal embryonic leucine zipper kinase (MELK) in mammary carcinogenesis through interaction with Bcl-G, a pro-apoptotic member of the Bcl-2 family.

Publications

Involvement of maternal embryonic leucine zipper kinase (MELK) in mammary carcinogenesis through interaction with Bcl-G, a pro-apoptotic member of the Bcl-2 family.

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