Metastasis of prostate cancer and melanoma cells in a preclinical in vivo mouse model is enhanced by L-plastin expression and phosphorylation

Abstract

BackgroundTumor cell migration and metastasis require dynamic rearrangements of the actin cytoskeleton. Interestingly, the F-actin cross-linking and stabilizing protein L-plastin, originally described as a leukocyte specific protein, is aberrantly expressed in several non-hematopoietic malignant tumors. Therefore, it has been discussed as a tumor marker. However, systematic in vivo analyses of the functional relevance of L-plastin for tumor cell metastasis were so far lacking.MethodsWe investigated the relevance of L-plastin expression and phosphorylation by ectopical expression of L-plastin in human melanoma cells (MV3) and knock-down of endogenous L-plastin in prostate cancer (PC3M). The growth and metastatic potential of tumor cells expressing no L-plastin, phosphorylatable or non-phosphorylatable L-plastin was analyzed in a preclinical mouse model after subcutaneous and intracardial injection of the tumor cells.ResultsKnock-down of endogenous L-plastin in human prostate carcinoma cells led to reduced tumor cell growth and metastasis. Vice versa, and in line with these findings, ectopic expression of L-plastin in L-plastin negative melanoma cells significantly increased the number of metastases. Strikingly, the metastasis promoting effect of L-plastin was not observed if a non-phosphorylatable L-plastin mutant was expressed.ConclusionsOur data provide the first in vivo evidence that expression of L-plastin promotes tumor metastasis and, importantly, that this effect depends on an additionally required phosphorylation of L-plastin. In conclusion, these findings imply that for determining the importance of tumor-associated proteins like L-plastin a characterization of posttranslational modifications is indispensable.

Proteotranscriptomic Profiling of 231-BR Breast Cancer Cells: Identification of Potential Biomarkers and Therapeutic Targets for Brain Metastasis

“…This protein is an actin filament cross-linker that has been shown to contribute to the fine-tuning of actin turnover in breast cancer cells, and its phosphorylation by PKC-delta has recently been shown to induce actin polymerization and tumor cell invasion (72). The expression of LCP1 enhances metastatic properties in both prostate cancer and melanoma cells (73) and this study indicates a potential link with brain metastasis as well.…”

L-Plastin promotes podosome longevity and supports macrophage motility

“…While LPL is not normally expressed outside cells of the immune system, over half of epithelial carcinomas and non-epithelial mesenchymal tumors examined ectopically expressed LPL (Delanote et al, 2005). Moreover, phosphorylation of LPL is associated with metastasis (Riplinger et al, 2014), and variant alleles of LPL have been associated with cancer progression (Ning et al, 2014). Recently, it has been shown that depletion of LPL can inhibit tissue invasion by prostate cancer cell lines, and ectopic expression of LPL can increase the metastatic potential of melanoma lines (Riplinger et al, 2014).…”

“…Moreover, phosphorylation of LPL is associated with metastasis (Riplinger et al, 2014), and variant alleles of LPL have been associated with cancer progression (Ning et al, 2014). Recently, it has been shown that depletion of LPL can inhibit tissue invasion by prostate cancer cell lines, and ectopic expression of LPL can increase the metastatic potential of melanoma lines (Riplinger et al, 2014). Macrophage podosomes resemble cancer cell invadopodia in certain ways, so improved understanding of the function of LPL in podosome biology may reveal new targets for prevention of cancer metastasis.…”

An NKX3.1 binding site polymorphism in the l-plastin promoter leads to differential gene expression in human prostate cancer

“…The L‐plastin isoform, which is abundantly expressed in hematopoietic cell lineages, is not active in most normal cells, but it is frequently activated and overexpressed in various types of human malignant solid tumors . The major functional domains of L‐plastin are two calcium‐binding sites, a calmodulin‐binding site, and two tandem actin‐binding domains . In vitro studies have indicated that L‐plastin is capable of bundling actin filaments through its actin‐binding domains and is regulated by phosphorylation of Ser5 .…”

“…We have previously reported that L‐plastin expression is upregulated by both estrogen and androgen exposure in a steroid‐hormone sensitive prostate cancer model and is associated with the malignant state in prostatic epithelial cells . Overexpression of L‐plastin was shown to be functionally involved in prostate cancer invasion and metastasis both in vitro and in vivo . However, hormone‐free cultured LNCaP cells and androgen‐insensitive prostate cancer cells (PC‐3) presented overexpression of the L‐plastin gene, suggesting that other non‐steroidal factors might promote its expression.…”