Disease relevance of GMNN

• In this report, we analyzed hCdt1, hCdc6, and hGeminin, the hCdt1 inhibitor expression, in a series of non-small-cell lung carcinomas, and investigated for putative relations with G(1)/S phase regulators, tumor kinetics, and ploidy [1].
• Human cytomegalovirus infection leads to accumulation of geminin and inhibition of the licensing of cellular DNA replication [2].
• We also transfected a full-length geminin cDNA in a human non-tumorigenic and a cancer breast cell lines and obtained derivatives expressing high levels of the protein [3].
• Moreover, geminin was expressed at higher level in 56% and 58% of colon and rectal cancers, respectively, compared with the corresponding adjacent normal mucosa [3].
• Expression of the licensing factors, Cdt1 and Geminin, in human colon cancer [4].

High impact information on GMNN

• Geminin inhibits DNA replication by preventing the incorporation of MCM complex into prereplication complex (pre-RC) [5].
• We propose that geminin inhibits DNA replication during S, G2, and M phases and that geminin destruction at the metaphase-anaphase transition permits replication in the succeeding cell cycle [5].
• Geminin, an inhibitor of DNA replication, is degraded during mitosis [5].
• In synchronized HeLa cells, geminin is absent during G1 phase, accumulates during S, G2, and M phases, and disappears at the time of the metaphase-anaphase transition [5].
• Inhibition of eukaryotic DNA replication by geminin binding to Cdt1 [6].

Chemical compound and disease context of GMNN

• PURPOSE: Gemcitabine (Gem) is the standard treatment for advanced pancreatic cancer [7].
• PATIENTS AND METHODS: In this multicenter phase II trial, patients with unresectable or metastatic PC who had progressed on single-agent Gem or a Gem-containing regimen received pemetrexed 500 mg/m(2) as a 10-min infusion every 3 weeks until disease progression or occurrence of unacceptable toxicity [8].
• In two recent randomised trials, gemcitabine plus cisplatin (Gem/Cis) was found to be at least as effective as vinorelbine plus cisplatin (Vin/Cis), paclitaxel plus cisplatin (Pac/Cis), paclitaxel plus carboplatin (Pac/Carbo), or docetaxel plus cisplatin (Doc/Cis) in patients with advanced non-small cell lung cancer (NSCLC) [9].
• Gemcitabine (Gem) is a deoxycytidine analog that is effective against pancreatic cancer and other malignancies following conversion to the 5'-O-mono-, di- and tri-phosphate forms [10].

Biological context of GMNN

• Here, we show that inactivation of Geminin, an inhibitor of origin licensing, leads to rereplication in human normal and tumor cells within the same cell cycle [11].
• These data show that Geminin is required for maintaining genomic stability in human cells [11].
• Taken together, these findings suggest that Cdt1 function is also negatively regulated by the Cdk phosphorylation independent of geminin binding [12].
• Geminin was downregulated, whereas cdt1 levels were maintained upon differentiation of both cell lines, independently of whether cells entered extra S-phases [13].
• Conversely, loss of Gem (in common with gain of Six3 (ref. 1)) promotes retinal precursor-cell proliferation and results in expanded optic vesicles, markedly potentiating Six3 gain-of-function phenotypes [14].

Anatomical context of GMNN

• Increased expression of geminin stimulates the growth of mammary epithelial cells and is a frequent event in human tumors [3].
• Moreover, both Cdt1 and Geminin expression are severely downregulated upon differentiation of Caco-2 cells, an in vitro model of intestinal epithelial differentiation [4].
• In situ hybridization and immunohistochemistry localize Cdt1 as well as geminin to the proliferative compartment of the developing mouse gut epithelium [15].
• Later, embryos expressing geminin have an expanded dorsal neural territory and ventral ectoderm is converted to neurons [16].
• Misexpression of geminin in gastrula ectoderm suppresses BMP4 expression and converts prospective epidermis into neural tissue [16].

Associations of GMNN with chemical compounds

• We show that truncated Geminin produced by cleavage at C1 can promote apoptosis [17].
• Although Gem expression is rare in epithelial and hematopoietic cancer cell lines, constitutive Gem levels were detected in several neuroblastoma cell lines and could be further induced as much as 10-fold following treatment with PMA or the acetylcholine muscarinic agonist, carbachol [18].
• Recent evidence indicates that Gemcitabine (Gem) may modulate ERCC1 nucleotide excision repair activity, and down-regulation of DNA repair activity by ERCC1 antisense RNA reportedly inhibits synergism of CDDP/Gem [19].
• Performance of Gem Premier blood gas/electrolyte analyzer evaluated [20].
• We have recently shown that Rad and Gem bind calmodulin in a Ca2+-dependent manner via this C-terminal extension, involving residues 278-297 in human Rad. This domain also contains several consensus sites for serine phosphorylation, and Rad is complexed with calmodulin-dependent protein kinase II (CaMKII) in C2C12 cells [21].

Physical interactions of GMNN

• In addition, geminin directly interacts with Six3 and Hox homeodomain proteins during embryogenesis and inhibits their functions [22].
• Contrary to existing in vitro data, we show that Cdt1 simultaneously binds Geminin and chromatin in vivo, thereby recruiting Geminin onto chromatin [23].

Enzymatic interactions of GMNN

• We also show that geminin becomes phosphorylated as S phase proceeds and identify by MALDI mass spectrometry two specific major phosphorylation sites [24].

Regulatory relationships of GMNN

• Loss of Geminin induces rereplication in the presence of functional p53 [11].
• Geminin inhibits cell-cycle progression by sequestering Cdt1 (refs 4, 5), the key component for the assembly of the pre-replication complex [14].
• It has been described that the replication regulator protein geminin is rapidly degraded at the end of mitosis and newly expressed at the beginning of the next S phase in the metazoan cell cycle [24].
• Geminin is widely expressed in several malignancies and the number of geminin-expressing cells is directly proportional to the cell proliferation index as measured by Ki-67 expression [25].

Other interactions of GMNN

• Rereplication by depletion of geminin is seen regardless of p53 status and activates a G2/M checkpoint [26].
• Here we report that geminin forms a parallel coiled-coil homodimer with atypical residues in the dimer interface [27].
• Cdt1 is rapidly degraded early in S phase, but geminin remains bound to the chromatin sites [28].
• In this study, we showed that the transcription of human Geminin and Cdt1, as well as that of MCM7, is activated by transcription factors E2F1-4, but not by factors E2F5-7 [29].
• Licensing is blocked at other cell cycle stages by the activity of cyclin-dependent kinases and a small protein called geminin [30].

Analytical, diagnostic and therapeutic context of GMNN

• Under these conditions, nearly all Cdt1 and a major part of geminin are bound to chromatin and reside at the same or closely adjacent sites as shown here by chromatin immunoprecipitation [28].
• A high expression of geminin was also detected by immunohistochemistry in 60% of human primary breast cancers [3].
• In this study, we evaluated by Western blot analysis the expression of geminin in a series of human cancer cell lines of various histogenetic origin and in a series of human primary colon, rectal, and breast cancers [3].
• Immunohistochemistry and immunoblotting for geminin, however, reveals that the protein is expressed specifically in proliferating lymphocytes and epithelial cells [25].
• Microinjection into Xenopus embryos demonstrated that import-deficient Gem was incapable of modulating ectodermal cell fate, but that this activity was rescued by fusion to a heterologous NLS [31].

References