1. ¹Department of Technology and Health, Istituto Superiore di Sanità, Rome, Italy
2. ²Department of Pathology and Experimental Medicine, University of Rome "La Sapienza," Rome, Italy
3. ³Department of Drug Research and Evaluation, Istituto Superiore di Sanità, Rome, Italy
4. ⁴Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy
5. ⁵Experimental Oncology Department, National Institute of Tumours, Fondazione "G. Pascale", Naples, Italy

Correspondence: Dr A. Molinari, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy. E-mail: agnese.molinari@iss.it

Received 18 October 2006; Revised 11 June 2007; Accepted 1 July 2007; Published online 18 October 2007.

Abstract

Malignant melanoma shows high levels of intrinsic drug resistance associated with a highly invasive phenotype. In this study, we investigated the role of the drug transporter P-glycoprotein (Pgp) in the invasion potential of drug-sensitive (M14 WT, Pgp-negative) and drug-resistant (M14 ADR, Pgp-positive) human melanoma cells. Coimmunoprecipitation experiments assessed the association of Pgp with the adhesion molecule CD44 in multidrug resistant (MDR) melanoma cells, compared with parental ones. In MDR cells, the two proteins colocalized in the plasma membrane as visualized by confocal microscopy and immunoelectron microscopy on ultrathin cryosections. MDR melanoma cells displayed a more invasive phenotype compared with parental cells, as demonstrated by quantitative transwell chamber invasion assay. This was accomplished by a different migration strategy adopted by resistant cells ("chain collective") previously described in tumor cells with high metastatic capacity. The Pgp molecule, after stimulation with specific antibodies, appeared to cooperate with CD44, through the activation of ERK1/2 and p38 mitogen-activated protein kinase (MAPK) proteins. This activation led to an increase of metalloproteinase (MMP-2, MMP-3, and MMP-9) mRNAs, and proteolytic activities, which are associated with an increased invasive behavior. RNA interference experiments further demonstrated Pgp involvement in migration and invasion of resistant melanoma cells. A link was identified between MDR transporter Pgp, and MAPK signaling and invasion.