DAPK is involved in the p dependent
DAPK-1 is involved in the p53 dependent apoptotic pathway and it is a mediator of γ-interferon induced apoptosis. DAPK-1 is also involved in other death signaling pathways (tumor necrosis factor-α, CD95 and transforming growth factor-β) and it blocks tumor metastasis in vivo. The loss of DAPK mRNA octopamine kinase in cases of promoter methylation was demonstrated in B-cell malignancies and nonsmall cell lung cancer. Using quantitative MSP we detected promoter methylation of DAPK-1 in 62% of cases. In accordance with findings by Wethkamp et al we also could not find a correlation of promoter methylation of the DAPK-1 gene with mRNA expression, or with tumor stage or grade. After integrating tumor size, lymph node involvement and metastatic tumor recurrence as additional characteristics we found that mRNA expression levels correlated with the presence of lymph node metastasis.
The TNM staging system is currently the most extensively used tool for providing prognostic information on RCC but data published in the last few years have led to significant controversies calling for more accurate and predictive prognostic factors. Not all patients in our study showed metastatic disease but of the 28 who did 15 had significantly lower mRNA levels of DAPK-1 in the tumor as well as in normal tissue.
The role of promoter methylation of the DAPK-1 gene in RCC is still not clear. In tumor samples a correlation between higher methylation levels and subsequent lower mRNA expression was not found. In vitro studies must show whether exposition to 5-Aza-CdR in DAPK-1 methylated RCC cell lines would lead to the re-expression of DAPK-1 on a transcriptional or translational level. Reu et al reported that reactivation of the epigenetically silenced RASSF1A gene by 5-Aza-CdR augments the cellular response to IFN treatment more than 10 times in RCC and melanoma cell lines. This suggests that an increase in DAPK-1 expression levels participating in IFN-γ induced apoptosis could positively influence the outcome of IFN-γ based immunomodulatory therapy.
Conclusions Our data suggest that increased DAPK-1 expression levels help prevent metastatic tumor development. The fact that APAF-1 and DAPK-1 mRNA expression levels are related to the development of metastatic disease emphasizes their relevance in the tumorigenesis of RCC. One might hypothesize that patients with large tumors and the absence of lymph node or metastatic disease at surgery would benefit from adjuvant therapy strategies when there is low APAF-1 and DAPK-1 expression. Moreover, reactivation of epigenetically silenced genes may reconstitute the ability of the cell to undergo apoptosis or potentiate the antitumor activity of immunomodulatory treatment strategies.
Introduction Calcium is a ubiquitous cellular signal that controls a plethora of cellular processes , . Information encoded in transient calcium signals is deciphered by various intracellular calcium-binding proteins (CaBPs) which exhibit calcium affinities and binding kinetics compatible with the intensities and duration of the calcium waves that can be elicited in the cytosol of eukaryotic cells . These CaBPs convert the signals into a wide variety of biochemical responses. Besides the calcium-buffers or transporters involved in calcium storage, an ensemble of proteins called calcium-sensors or transducers are integral parts of signaling cascades and convey the calcium signal to trigger the appropriate biochemical and cellular responses , . Among this ensemble, calmodulin, a member of the family of proteins containing EF-hands is the most prominent example used to discuss the determinants of target selectivity , . Calmodulin (CaM) is a multifunctional calcium transducer . It functions as a central regulator of cellular metabolism in response to changes in cellular calcium levels by interacting with various targets . Numerous studies have been devoted to the understanding CaM mechanism of action. Early models considered CaM as a simple off/on switch, in which apoCaM was inactive whereas the fully Ca2+ saturated protein allowed interaction with and activation of the various target enzymes. However both 1) the observation, namely with biophysical studies, that CaM Ca2+ binding sites were not equivalent and independent and 2) the steadily increasing number of target proteins and enzymes regulated by CaM, led to postulate a model in which CaM activity was regulated by the number of Ca2+ ions bound to it . Further refinement of the model included spatio-temporal and genetic regulations , . It is now generally admitted that CaM is highly flexible, this flexibility sustaining the multi-functionality of the protein . Nevertheless, the precise mechanism underlying integration of a calcium signal by CaM into a quantitative biochemical process and a specific cellular response is still unclear.