Chronic treatment with insulin-like growth factor I enhances myocyte contraction by upregulation of Akt-SERCA2a signaling pathway

Chronic treatment with insulin-like growth factor I (IGF-I) improves contractile function in congestive heart failure and ischemic cardiomyopathy. The present study investigated the effect of chronic treatment with IGF-I on intrinsic myocyte function and the role of the phosphatidylinositol (PI)3-kinase-Akt-sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a signaling cascade in these responses. Myocytes were isolated from 23 adult rats and cultured with and without IGF-I (10−6 M). After 48 h of treatment, myocyte function was evaluated. IGF-I increased contractile function (percent contraction, 7.7 ± 0.3% vs. 4.5 ± 0.3%; P < 0.01) and accelerated relaxation time (time for 70% relengthening, 81 ± 4 vs. 106 ± 5 ms; P < 0.05) compared with untreated myocytes [control (Con)]. The enhanced function was associated with an increase in Ca2+ transients assessed by fura-2 (340/380 nm; IGF-I, 0.42 ± 0.02 vs. Con, 0.25 ± 0.01; P < 0.01). The PI3-kinase inhibitor LY-249002 (10−9 M) abolished the enhanced function caused by IGF-I. IGF-I increased both Akt and SERCA2a protein levels 2.5- and 4.8-fold, respectively, compared with those of Con ( P < 0.01); neither phospholamban nor calsequestrin was affected. To evaluate whether the SERCA2a protein was directly mediated by Akt-SERCA2a signaling, IGF-I-induced changes in the SERCA2a protein were compared in myocytes transfected with adenovirus harboring either constitutively active Akt [multiplicity of infection (MOI), 15] or dominant negative Akt (dnAkt; MOI, 15). The ability of IGF-I to upregulate the SERCA2a protein in myocytes transected with active Akt was absent in dnAkt myocytes. Taken together, our findings indicate that chronic treatment with IGF-I enhances intrinsic myocyte function and that this effect is due to an enhancement in intracellular Ca2+ handling, secondary to the activation of the PI3-kinase-Akt-SERCA2a signaling cascade.

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Increased Expression of Insulin-Like Growth Factor I Is Associated with Ara-C Resistance in Leukemia.

Blood ◽

10.1182/blood.v106.11.1513.1513 ◽

2005 ◽

Vol 106 (11) ◽

pp. 1513-1513

Author(s):

Shori Abe ◽

Hideo Harigae ◽

Tadao Funato ◽

Junichi Kameoka ◽

Shinichiro Takahashi ◽

...

Keyword(s):

Growth Factor ◽

Biological Significance ◽

Pi3 Kinase ◽

Expression Level ◽

Akt Pathway ◽

Clinical Samples ◽

Insulin Like Growth Factor ◽

Factor I ◽

Igf I ◽

Growth Factor I

Abstract Cytosine arabinoside (Ara-C) is one of the most common drugs used in the treatment of acute myeloid leukemia (AML). Therefore, the resistance to Ara-C is a major obstacle to improvement of the cure rate of AML. However, the molecular mechanism for Ara-C resistance has not been fully understood. In order to investigate the mechanism involved in Ara-C resistance, the gene expression profile of Ara-C-resistant human K562 leukemia cells (K562/AC cells) was compared with that of the Ara-C-sensitive K562 parental cells by using a cDNA microarray platform. Correspondence analysis demonstrated that the insulin-like growth factor I (IGF-I) gene was significantly upregulated in K562/AC cells. The increased expression of IGF-I in K562/AC cells was confirmed by quantitative RT-PCR (RQ-PCR). We then studied the biological significance of IGF-I upregulation in Ara-C resistance. First, K562/AC cells were treated by suramin, a nonspecific growth factor antagonist. The treatment with suramine reduced viability and induced apoptosis of K562/AC cells. Furthermore, the addition of IGF-I neutralizing antibody exhibited the same effect as suramine. Moreover, the IC50 of Ara-C sensitive K562 parental cells was increased by the addition of exogenous IGF-I ligand. These results strongly suggest that IGF-I-IGF-I-R pathway is directly involved in Ara-C resistance. Next, the activation status of phosphatidylinositol 3-kinase (PI3-kinase)/Akt pathway, which is the downstream of IGF-I-IGFI-R signal, in K562/AC cells was examined. Western blot analysis showed that the phosphorylation level of Akt is higher in K562/AC cells than K562 sensitive cells. In addition, LY294002, the specific inhibitor for PI3-kinase reduced the survival of K562/AC cells. Since activation of PI3-kinase/Akt pathway has been shown to exhibit an anti-apoptotic effect in tumor cells, it is possible that IGF-I induces Ara-C resistance by escaping from apoptosis through PI3-kinase/Akt pathway in an autocrine or paracrine fashion. Finally, the expression level of IGF-I was examined in 27 clinical samples by RQ-PCR. The results showed that IGF-I expression level was higher in leukemic cells in refractory or relapsed AML patients, who received Ara-C combined chemotherapy, than that at diagnosis. These results suggest that the inhibition of the IGF-I-IGF-I receptor pathway is a valuable therapeutic approach to overcome Ara-C resistance in AML.

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Antiapoptotic signalling by the insulin-like growth factor I receptor, phosphatidylinositol 3-kinase, and Akt.

Molecular and Cellular Biology ◽

10.1128/mcb.17.3.1595 ◽

1997 ◽

Vol 17 (3) ◽

pp. 1595-1606 ◽

Cited By ~ 730

Author(s):

G Kulik ◽

A Klippel ◽

M J Weber

Keyword(s):

Growth Factor ◽

Protein Kinase ◽

Tyrosine Kinases ◽

Pi3 Kinase ◽

Insulin Like Growth Factor ◽

Phosphatidylinositol 3 Kinase ◽

Factor I ◽

Igf I ◽

Growth Factor I ◽

Phosphatidylinositol 3

We have found that insulin-like growth factor I (IGF-I) can protect fibroblasts from apoptosis induced by UV-B light. Antiapoptotic signalling by the IGF-I receptor depended on receptor kinase activity, as cells overexpressing kinase-defective receptor mutants could not be protected by IGF-I. Overexpression of a kinase-defective receptor which contained a mutation in the ATP binding loop functioned as a dominant negative and sensitized cells to apoptosis. The antiapoptotic capacity of the IGF-I receptor was not shared by other growth factors tested, including epidermal growth factor (EGF) and thrombin, although the cells expressed functional receptors for all the agonists. However, EGF was antiapoptotic for cells overexpressing the EGF receptor, and expression of activated pp60v-src also was protective. There was no correlation between protection from apoptosis and activation of mitogen-activated protein kinase, p38/HOG1, or p70S6 kinase. On the other hand, protection by any of the tyrosine kinases against UV-induced apoptosis was blocked by wortmannin, implying a role for phosphatidylinositol 3-kinase (PI3 kinase). To test this, we transiently expressed constitutively active or kinase-dead PI3 kinase and found that overexpression of activated phosphatidylinositol 3-kinase (PI3 kinase) was sufficient to provide protection against apoptosis. Because Akt/PKB is believed to be a downstream effector for PI3 kinase, we also examined the role of this serine/threonine protein kinase in antiapoptotic signalling. We found that membrane-targeted Akt was sufficient to protect against apoptosis but that kinase-dead Akt was not. We conclude that the endogenous IGF-I receptor has a specific antiapoptotic signalling capacity, that overexpression of other tyrosine kinases can allow them also to be antiapoptotic, and that activation of PI3 kinase and Akt is sufficient for antiapoptotic signalling.

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