e, rt – qpcr for inhba, il6, acta2 and col1a1 relative to rpl27 using rna from mitocepted or mock - treated hpfs ( n = 3 cultures per group ). f, fluidfm experimental setup, adapted from a previous study. g, image of fluidfm - mediated injection of mitochondria into hpfs. h, percentage of ki67 fibroblasts in hpfs injected with a431 - derived mitochondria using fluidfm or mock treatment ( n = 3 cultures per group ). i, rt – qpcr for inhba using rna from hpfs subjected to mitoception with mitochondria from hacat, hacat - ras or a431 cell lines ( n = 3 cultures per cell line ). j, rt – qpcr for inhba using rna from ( 1 ) mock - treated hpfs or hpfs subjected to mitoception with mitochondria ( 2 ) from keratinocytes of a healthy individual, ( 3 ) from normal keratinocytes of a person with scc or ( 4 ) malignant cancer cells of the same person with scc. right, representative fn1 – coli immunoflu orescence stainings with quantification of staining intensity in the decm produced by hpfs after mitoception with mitochondria from the different primary donor cells ( n = 3 mitoceptions per cell type ). k, percentage of ki67 hpfs subjected to mitoception with different amounts of mitochondria isolated from a431 cells. numbers on the x axis show the ratio of donor a431 cells ( used for mitochondrial isolation ) and recipient hpfs ( n = 3 cultures per group ). graphs show the mean ± s. e. m. an unpaired two - sided student ’ s t - test ( b, d, e, h ) or two - sided one - way anova with bonferroni post hoc multiple comparison test ( i – k ) was used to determine statistical significance. scale bars, 100 μm ( a, j ), 10 μm ( c ) and 25 μm ( g ). source data we found that, 24 h after mitoception with mitotracker - labeled a431 mitochondria, the proliferation rate was significantly higher compared to mock - treated hpfs ( fig. 4d ) and the mitocepted cells showed higher expression of caf genes ( fig. 4e and extended data fig. 4a ). by contrast, expression of three selected isgs was not increased after mitoception ( extended data fig. 4b ), suggesting that mitochondrial transfer alone is not sufficient to activate these genes. to validate the effect of purified mitochondria on caf differentiation, we used fluid force microscopy ( fluidfm ) to inject purified mitotracker green - stained a431 mitochondria directly into the cytoplasm of hpfs ( fig. 4f, g ). the injected hpfs also showed increased proliferation ( fig. 4h ), again demonstrating that the effect of mitochondria on the induction of caf features is independent of the mode of uptake. we next compared the effect of mitochondria isolated from the hacat keratinocyte cell line, their malignant counterpart hacat - ras and the highly malignant a431 cell line on hpfs in mitoception experiments using mitochondria isolated from the same number of cells. this normalization is justified because of the similar protein content of the mitochondrial isolates from all cell lines ( extended data fig. 4c ). the expression of inhba in the recipient hpfs increased in accordance with the malignancy of the donor cell line ( fig. 4i ). consistently, mitocepted fibroblasts, which received mitochondria from primary donor - derived scc cells, displayed increased expression of inhba compared to fibroblasts, which received mitochondria from adjacent nontransformed keratinocytes or from keratinocytes of a healthy individual, and deposited more fn1 and coli ( fig. 4j ). the effect of mitochondria on hpfs was concentration dependent. mitoception of hpfs with a431 mitochondria at a 1: 1 ratio ( same number of donor a431 cells and recipient hpfs ) caused a significant increase in hpf proliferation, while lower amounts of mitochondria had only a minor effect. a further increase in the amount of mitocepted mitochondria did not further promote hpf proliferation ( fig. 4k ). to gain mechanistic insight into the alterations in hpfs that occur upon mitochondrial transfer from cancer cells, we measured their oxygen consumption rate ( ocr ) using seahorse analysis. transplantation of a431 - derived but not hacat cell - derived mitochondria promoted basal respiration and proton leak in the recipient fibroblasts ( fig. 5a, b and extended data fig. 4d ). the values observed in hpfs after mitoception with a431 mitochondria almost reached those observed in a431 cells ( fig. 5a, b ). mitochondria from hacat - ras cells also promoted proton leak but had no effect on basal respiration ( extended data fig. 4e ). these findings provide a possible explanation for the higher proliferation of recipient hpfs because increased oxidative phosphorylation ( oxphos ) in cultured fibroblasts was shown to promote their proliferation. consistently, inhibition of oxphos in hpfs by oligomycin prevented the increase in caf marker expression and proliferation after transplantation of a431 mitochondria ( extended data fig. 4f, g ). high ocr and atp levels in cafs are also important for their release of protumorigenic factors. consistently, cm from fibroblasts, which received a431 mitochondria using mitoception, promoted proliferation and transwell migration of a431 cells to a significantly higher extent compared to cm from control ( mock - treated ) fibroblasts ( fig. 5c ). fig. 5functional cancer cell mitochondria are required for caf reprogramming. a, basal respiration of hpfs subjected to mitoception with a431 or hacat mitochondria or mock treatment in comparison to a431 cells ( n = 5 independent mitoceptions per cell type ). b, proton leak in the same cultures as in a. c, percentage of ki67 a431 cells and transwell migration of a431 cells cultured in cm of mitocepted or mock - treated hpfs ( n = 3 cultures per group ). d, rt – qpcr for inhba and il6 using rna from mitocepted ( mitochondria from mda - mb - 231 breast cancer cells ) or mock - treated hpfs ( n = 3 cultures per group ). e, clonogenicity of mda - mb - 231 cells cultured in cm from hpfs subjected to mitoception with mitotracker green - stained mitochondria from mda - mb - 231 cells or mock treatment ( n = 3 cultures per treatment group ). f, representative image of 3 - week - old ear xenograft tumors ( arrowheads ) following intradermal coinjection of a431 cells and mitocepted ( with a431 mitochondria ) or mock - treated hpfs and tumor volume at various time points ( n = 5 tumors per group from different mice ). g, representative immunoflu orescence stainings of tumors formed by a431 cells and mitocepted or mock - treated hpfs for e - cadherin and fn1 ( green ) and meca32 ( red ), counterstained with hoechst ( blue ) ( n = 5 tumors per group from different mice ). h, percentage of ki67 hpfs subjected to mitoception with a431 lmt mitochondria or mock treatment and rt – qpcr for inhba using rna from hpfs subjected to mitoception with a431 lmt mitochondria or mock treatment ( n = 9 ki67 or n = 3 rt – qpcr cultures per treatment group ). i, percentage of ki67 a431 cells ( left ) or transwell migration of a431 cells ( right ) cultured in cm from hpfs subjected to mitoception with a431 lmt mitochondria or mock treatment ( n = 9 ki67 or n = 3 transwell migration cultures per treatment group ). j, left, tumor volume at various time points during tumor development by a431 cancer cells coinjected with mitocepted hpfs, which received mitochondria from control or lmt a431 cells ( n = 4 tumors per group from different mice ). right, histological stainings of a tumor from each group. graphs show the mean ± s. e. m. an unpaired two - sided student ’ s t - test ( c – e, h, i ) or two - sided one - way ( a, b ) or two - way ( f, j ) anova with bonferroni post hoc multiple comparison test was used to determine statistical significance. scale bars, 200 μm ( g ) and 1 mm ( j ). source data a, basal respiration of hpfs subjected to mitoception with a431 or hacat mitochondria or mock treatment in comparison to a431 cells ( n = 5 independent mitoceptions per cell type ).