Abstract
Translocation to the nucleus of diacylglycerol kinase (DGK)– ζ is dependent on a sequence homologous to the effector domain of Myristoylated Alanine Rich C-Kinase Substrate (MARCKS). These data would suggest that MARCKS could also localize to the nucleus. A single report demonstrated immunofluorescence staining of MARCKS in the nucleus; however, further experimental evidence confirming the specific domain responsible for this localization has not been reported. Here, we report that MARCKS is present in the nucleus in GBM cell lines. We then over-expressed wild-type MARCKS (WT) and MARCKS with the effector domain deleted (ΔED), both tagged with V5-epitope in a GBM cell line with low endogenous MARCKS expression (U87). We found that MARCKS-WT localized to the nucleus, while the MARCKS construct without the effector domain remained in the cytoplasm. We also found that over-expression of MARCKS-WT resulted in a significant increase in total cellular phosphatidyl-inositol (4,5) bisphosphate (PIP2) levels, consistent with prior evidence that MARCKS can regulate PIP2 levels. We also found increased staining for PIP2 in the nucleus with MARCKS-WT over-expression compared to MARCKS ΔED by immunofluorescence. Interestingly, we observed MARCKS and PIP2 co-localization in the nucleus. Lastly, we found changes in gene expression when MARCKS was not present in the nucleus (MARCKS ΔED). These data indicate that the MARCKS effector domain can function as a nuclear localization signal and that this sequence is critical for the ability of MARCKS to regulate PIP2 levels, nuclear localization, and gene expression. These data suggests a novel role for MARCKS in regulating nuclear functions such as gene expression.
Highlights
Myristoylated Alanine Rich C-Kinase Substrate (MARCKS) is an intrinsically unstructured protein that has been observed to influence numerous cellular processes including migration, proliferation, and survival [1,2,3,4]
The MARCKS Effector Domain has homology with known nuclear localization sequences Based on the novel findings of MARCKS in the nucleus of cancer cells, we examined the literature and MARCKS amino acid sequence to try to identify a potential nuclear localization sequence (NLS)
Our study shows for the first time, endogenous MARCKS being present in the nucleus, in Glioblastoma multiforme (GBM) cells
Summary
MARCKS is an intrinsically unstructured protein that has been observed to influence numerous cellular processes including migration, proliferation, and survival [1,2,3,4]. That MARCKS circulates from the plasma membrane to the cytoplasm back to the plasma membrane by reversible cycles of phosphorylation and de-phosphorylation; or by reversible cycles of calmodulin binding [5] It is through this process by which MARCKS has been shown to reversibly sequester the phospholipid phosphatidyl-inositol (4,5) bisphosphate (PIP2). This process has been implicated in the regulation of the actin cytoskeletal dynamics, among other processes including spermatozoa acrosomal exocytosis [6], Akt signaling [1,7], and mitosis regulation [8]. The data present here provides novel findings regarding MARCKS’ ability to migrate into the nucleus and regulate nuclear PIP2
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