Genotypic diversity drives disease progression, with different sub-clones having differing capacities for proliferation, invasion and metastasis (Pon & Marra 2015, Kumar & Abbas 2014). Differentiation is affected by intercellular cytoplasmic exchange via plasmodesmata, septal pores and tunneling nanotubes, in plants, fungi and animals respectively (Bloemendal & Kuck 2013, Gerdes et al. 2013, Caneparo et al. 2011). We earlier reported extensive exchange of cytoplasm between fibroblasts and malignant cells (MC) in co-culture (David et al. 2012), but the structures responsible and phenotypic effects remained unknown.
Using DiD and DiO as indelible lipophilic fluorescent markers for organelles and plasma membrane, we demonstrated transfer of organelles primarily from human dermal fibroblasts (HDF) to MC by both time-lapse confocal microscopy and FACS analysis. Image analysis of co-cultures of HDF with a range of MC cell lines, revealed that uptake of fibroblast label by MC in co-culture resulted in altered MC morphology, with increased cell circularity and cell profile area (p < 0.025), the cell lines studied being: SAOS-2 and U2OS osteosarcoma cells; PEO1, PEO4, and COLO316 ovarian carcinoma cells, and NM200-B12, WMM175 and NM39 melanoma cells.
We further compared MC with high as opposed to low HDF labeling following separation by FACS sorting, and found uptake of HDF label reduced MC proliferation and increased MC migration, using SAOS-2 in most experiments (p < 0.004), but also H3122 lung cancer and A573 osteosarcoma cells.
Using a stiffness profile scanning atomic force microscopy approach (Zoellner et al. 2015), we demonstrated SAOS-2 with low stiffness accepted more HDF label than those with high stiffness, and also had greater cell height (p < 0.0001), suggesting a possible hydrodynamic mechanism.
Data demonstrate increased MC phenotypic diversity through uptake of fibroblast contents via filopodia.