Cell type dependent effects of HOTAIR overexpression on proliferation and clonogenicity. (a) The relative number of vital cells was monitored in quadruplicates of stably HOTAIR-transfected VM-CUB1 and 5637 cell clones by MTT assay over 4 days. Results shown for one assay are representative for three independent assays (**p ≤ 0.001). (b) Effects of HOTAIR transfection on clonogenicity in VM-CUB1 or 5637 cells. (c) Representative picture from increased anchorage-independent growth of VM-CUB1_HOTAIR 20 cells in triplicate soft agar assays (4 x (top) and 20 x (center) magnification); 5637 cells poorly formed colonies independent of HOTAIR overexpression (20x, bottom). (d) MTT assays for additional stably transfected HOTAIR clones of VM-CUB1 and 5637, with analogous results to those shown in (a). Number of vital cells was determined in quadruplicate at every time point for every clone. For p-values see Additional file 2: Table S1. (e, f) Cell-type dependent effects of HOTAIR on clonogenicity in further UC cell lines (*p ≤ 0.05, ** ≤ 0.001).