Wen-Liang Kuo

Raf, but not MEK or ERK, is sufficient for differentiation of hippocampal neuronal cells.

To elucidate signal transduction pathways leading to neuronal differentiation, we have investigated a conditionally immortalized cell line from rat hippocampal neurons (H19-7) that express a temperature sensitive simian virus 40 large T antigen. Treatment of H19-7 cells with the differentiating agent basic fibroblast growth factor at 39 degrees C, the nonpermissive temperature for T function, resulted in the activation of c-Raf-1, MEK, and mitogen-activated protein (MAP) kinases (ERK1 and -2). To evaluate the role of Raf-1 in neuronal cell differentiation, we stably transfected H19-7 cells with v-raf or an oncogenic human Raf-1-estrogen receptor fusion gene (deltaRaf-1:ER). deltaRaf-1:ER transfectants in the presence of estradiol for 1 to 2 days expressed a differentiation phenotype only at the nonpermissive temperature. However, extended exposure of the deltaRaf-1:ER transfectants to estradiol or stable expression of the v-raf construct yielded cells that extended processes at the permissive as well as the nonpermissive temperature, suggesting that cells expressing the large T antigen are capable of responding to the Raf differentiation signal. deltaRaf-1:ER, MEK, and MAP kinase activities in the deltaRaf-1:ER cells were elevated constitutively for up to 36 h of estradiol treatment at the permissive temperature. At the nonpermissive temperature, MEK and ERKs were activated to a significantly lesser extent, suggesting that prolonged MAP kinase activation may not be sufficient for differentiation. To test this possibility, H19-7 cells were transfected or microinjected with constitutively activated MEK. The results indicate that prolonged activation of MEK or MAP kinases (ERK1 and -2) is not sufficient for differentiation of H19-7 neuronal cells and raise the possibility that an alternative signaling pathway is required for differentiation of H19-7 cells by Raf.

Differentiation of central nervous system neuronal cells by fibroblast-derived growth factor requires at least two signaling pathways: roles for Ras and Src.

To evaluate the role of mitogen-activated protein (MAP) kinase and other signaling pathways in neuronal cell differentiation by basic fibroblast-derived growth factor (bFGF), we used a conditionally immortalized cell line from rat hippocampal neurons (H19-7). Previous studies have shown that activation of MAP kinase kinase (MEK) is insufficient to induce neuronal differentiation of H19-7 cells. To test the requirement for MEK and MAP kinase (ERK1 and ERK2), H19-7 cells were treated with the MEK inhibitor PD098059. Although the MEK inhibitor blocked the induction of differentiation by constitutively activated Raf, the H19-7 cells still underwent differentiation by bFGF. These results suggest that an alternative pathway is utilized by bFGF for differentiation of the hippocampal neuronal cells. Expression in the H19-7 cells of a dominant-negative Ras (N17-Ras) or Raf (C4-Raf) blocked differentiation by bFGF, suggesting that Ras and probably Raf are required. Expression of dominant-negative Src (pcSrc295Arg) or microinjection of an anti-Src antibody blocked differentiation by bFGF in H19-7 cells, indicating that bFGF also signals through a Src kinase-mediated pathway. Although neither constitutively activated MEK (MEK-2E) nor v-Src was sufficient individually to differentiate the H19-7 cells, coexpression of constitutively activated MEK and v-Src induced neurite outgrowth. These results suggest that (i) activation of MAP kinase (ERK1 and ERK2) is neither necessary nor sufficient for differentiation by bFGF; (ii) activation of Src kinases is necessary but not sufficient for differentiation by bFGF; and (iii) differentiation of H19-7 neuronal cells by bFGF requires at least two signaling pathways activated by Ras and Src.

Effect of complementary pathway blockade on efficacy of combination enzastaurin and rapamycin

Rapamycin is an mTOR inhibitor with preclinical efficacy in squamous cell carcinoma of the head and neck (SCCHN). However, mTOR inhibitors also increase Akt activity in SCCHN cell lines, which would promote survival and oncogenesis. Enzastaurin is an AGC kinase inhibitor with nanomolar inhibitory concentrations for Akt and protein kinase C (PKC). Moreover, Akt and PKC inhibitors have demonstrated efficacy in SCCHN.

Efficacy of the Multi-Kinase Inhibitor Enzastaurin Is Dependent on Cellular Signaling Context

The number of targeted small molecules being developed in oncology is increasing rapidly. Many of these are designed to inhibit multiple kinases, and thus the mechanisms of responsiveness and predictive biomarkers can be difficult to discern. In fact, with few exceptions, multi-kinase inhibitors are developed with limited mechanism-based patient selection. Enzastaurin is a multi-kinase inhibitor being studied in several malignancies that we hypothesized would be active in squamous cell carcinoma of the head and neck, because it inhibits classic and novel protein kinase C isoforms. Indeed, enzastaurin reduced the growth of SQ-20B and CAL27 tumor xenografts, decreased proliferation in these cell lines, inhibited putative target phosphorylation, and induced cell cycle arrest. Gene expression arrays confirmed that expression of cell cycle genes, including cyclins D and E, were significantly altered by exposure to enzastaurin. However, testing a panel of squamous cell carcinoma of the head and neck cell lines revealed variable sensitivity to enzastaurin, which correlated significantly with baseline cyclin D1 protein expression. Moreover, sensitivity and resistance could be reversed, respectively, by expression or depletion of cyclin D1. Furthermore, analysis of sensitive and resistant cell lines revealed distinct differences in cyclin D1 regulation. Enzastaurin modulated cyclin D1 synthesis through an Akt-regulated pathway in the former, whereas high-level CCND1 gene amplification was present in the latter. These results underscore the critical relevance of cellular signaling context in developing cancer therapies in general and suggest that enzastaurin in particular would be most effective in tumors where baseline cyclin D1 expression is low to moderate and physiologically regulated. Mol Cancer Ther; 9(10); 2814–24. ©2010 AACR.

p62/SQSTM1 accumulation in squamous cell carcinoma of head and neck predicts sensitivity to phosphatidylinositol 3-kinase pathway inhibitors.

The phosphoinositol-3 kinase (PI3K) pathway is highly dysregulated in squamous cell carcinoma of the head and neck (SCCHN). While inhibitors of the PI3K/AKT pathway are being developed in cancer, their efficacy does not appear to be related to the presence of mutations or amplification in pathway genes. The PI3K pathway is a major regulator of macro-autophagy, an evolutionarily conserved catabolic process that degrades cellular materials to promote cellular homeostasis and survival under stress. Employing a panel of SCCHN cell lines, we observed a significant correlation between the activity of PI3K/AKT inhibitors and their ability to induce autophagy. More specifically, resistance to these inhibitors was associated with accumulation of p62/SQSTM1, a pleotropic protein that is consumed during autophagy, while loss of autophagy was, for the first time, found to be due to silencing of an essential autophagy gene, ATG7. Moreover, modulating ATG7 and p62/SQSTM1 could regulate sensitivity to PI3K/AKT inhibitors, underscoring a mechanistic link between autophagy and drug sensitivity. Analysis of human tissues revealed progressive accumulation of p62/SQSTM1 in a significant proportion of cancer samples compared to normal tissue, suggesting that defective autophagy has relevance to SCCHN. These findings are further validated by analysis of TCGA data confirming homozygous deletion and mRNA down-regulation of ATG7 in 10.0% of SCCHN samples. Taken together, these data indicate that p62/SQSTM1 levels modulate sensitivity to PI3K/AKT inhibitors; cancers vary in their capacity to undergo autophagy through epigenetic modification and, when deficient, accumulate p62/SQSTM1; and expression of autophagy-related proteins may serve as markers for resistance to PI3K/AKT inhibitors in SCCHN.

Localization of the gene encoding insulin-degrading enzyme to human chromosome 10, bands q23→q25

Insulin-degrading enzyme (IDE) is a cytosolic proteinase involved in the cellular processing of insulin. Using somatic cell hybrid analysis and in situ chromosomal hybridization, we have localized the gene encoding IDE to human chromosome 10, bands q23----q25. The murine Ide gene was previously mapped to Chromosome 19; together, these results suggest that the IDE gene is a member of a conserved syntenic group on human chromosome 10, bands q23----q25 and mouse Chromosome 19.

Immunohistochemical evidence of ubiquitous distribution of the metalloendoprotease insulin-degrading enzyme (IDE; insulysin) in human non-malignant tissues and tumor cell lines.

Abstract Immunohistochemical evidence of ubiquitous distribution of the metalloprotease insulin-degrading enzyme (IDE; insulysin) in human non-malignant tissues and tumor cells is presented. Immunohistochemical staining was performed on a multi-organ tissue microarray (pancreas, lung, kidney, central/peripheral nervous system, liver, breast, placenta, myocardium, striated muscle, bone marrow, thymus, and spleen) and on a cell microarray of 31 tumor cell lines of different origin, as well as trophoblast cells and normal blood lymphocytes and granulocytes. IDE protein was expressed in all the tissues assessed and all the tumor cell lines except for Raji and HL-60. Trophoblast cells and granulocytes, but not normal lymphocytes, were also IDE-positive.

Abstract 316: Modifying autophagy through combination treatments as a potential therapeutic strategy in head and neck squamous cell carcinoma (HNSCC)

Introduction: Autophagy, a catabolic process, can play a crucial role in cancer cell survival. Modifying this process has shown to be an effective mechanism of inducing cell death. In order to explore this concept, we induced autophagy with one agent (Akt-inhibitor MK-2206), and decreased autophagosomal trafficking with other agents (Paclitaxel and Nocadazole) by disrupting the microtubule networks. We hypothesized that by modifying autophagy through this combination, it would lead to an accumulation of autophagosomes and eventual cell death in a synergistic manner. Methods: SCC 61 and Cal 27 HNSCC cell lines were used to explore this hypothesis. SCC 61 cells were transduced with an m-Cherry GFP LC3B vector in order to detect autophagosomes under both fixed and live cell confocal microscopy. Cell viability and apoptosis assays were performed. A siRNA ATG 7 KO SCC 61 cell line was used to detect if in fact autophagy was important for this therapeutic approach. Results: There was an accumulation of autophagosomes with the combination of an Akt inhibitor and microtubule disrupters. A decrease in fusion of autophagosome to lysosome was seen when cells were treated with an agent, which disrupted the microtubule networks (Paclitaxel) but even more dramatically when treated with the combination (MK-2206 and Paclitaxel). Moreover, accumulation of autophagosomes occurred prior to induction of apoptosis with combination treatment. These effects were decreased with siRNA ATG 7 KO in SCC 61 cells, which were more resistant to combination treatment compared to control. Discussion: Manipulating autophagy with Akt inhibition (induction) and Paclitaxel (decreasing autophagic trafficking) leads to an accumulation of autophagosomes and eventual cell death in a synergistic manner. This therapeutic approach of altering the normal autophagic process warrants further investigation. Citation Format: Omar G. Ahmed, Wen-Liang Kuo, Tai-Fen Wei, Jeannette S. Messer, Marina Sharifi, Madhavi Nagilla, Kay Macleod, Ezra E.W. Cohen. Modifying autophagy through combination treatments as a potential therapeutic strategy in head and neck squamous cell carcinoma (HNSCC). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 316. doi:10.1158/1538-7445.AM2014-316