Abstract Nuclear size and morphology are distinct cancer features that pathologists use for diagnostic purposes. Proteins that regulate nuclear size have been identified in Xenopus, where nuclear import rates correlate with nuclear size. The levels of two nuclear import factors, importin α and NTF2, were shown to be particularly important in nuclear size regulation. It has also been shown that importin α2 is a potential biomarker in non-small cell lung cancer, as well as importin α1 in breast cancer. Our data implicate that NTF2 is a possible cancer biomarker. Our main goal is to analyze how these nuclear scaling factors affect nuclear size during carcinogenesis and to test how nuclear size impacts cancer growth characteristics. We find that manipulating the levels of importin α2 and NTF2 in HeLa and MRC-5 cells leads to altered nuclear size, demonstrating a conserved function for these factors in nuclear size regulation. To place these results in a cancer context, we are focusing on melanoma cell lines, including radial and vertical growth primary melanomas and metastatic melanomas. We find that, compared to normal melanocytes, the nuclear-to-cytoplasmic (N/C) volume ratio is increased in the cancer cell lines. Western blot analysis revealed an inverse correlation between NTF2 protein levels and nuclear size. We confirmed these results using a melanoma tissue microarray, finding similar differences in nuclear size and NTF2 expression levels between benign nevi and melanomas. We next performed transient transfection experiments with our melanoma cell lines. Importin α2 knock down led to smaller nuclear size, while knocking down the levels of NTF2 increased nuclear size, consistent with our Xenopus results. We also observed reduced nuclear size when NTF2 was ectopically expressed. Currently we are generating stable, inducible melanoma cell lines where we can precisely alter NTF2 and importin α expression levels using doxycycline. We will use these inducible cell lines to examine how altering nuclear size impacts cell proliferation rates, invasiveness, and apoptosis. We will also investigate how nuclear size affects gene positioning using FISH, focusing on genes involved in melanoma formation and metastasis. In the long term, we plan to move these studies into a mouse model where we can test how nuclear size affects in vivo metastatic capacity. Citation Format: Lidija D. Vukovic, Bradley A. Stohr, Dan L. Levy. NTF2 regulates nuclear size in mammalian cells and may contribute to altered nuclear size in melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 475.