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Three-dimensional (3D) cell culture is well documented to regain intrinsic metabolic properties and to bettermimic the in vivo situation than two-dimensional (2D) cell culture. Particularly, proline metabolism is critical for tumorigenesis since pyrroline-5-carboxylate (P5C) reductase (PYCR/P5CR) is highly expressed in various tumors and its enzymatic activity is essential for in vitro 3D tumor cell growth and in vivo tumorigenesis. PYCR converts the P5C intermediate to proline as a biosynthesis pathway, whereas proline dehydrogenase (PRODH) breaks down proline to P5C as a degradation pathway. Intriguingly, expressions of proline biosynthesis PYCR gene and proline degradation PRODH gene are up-regulated directly by c-Myc oncoprotein and p53 tumor suppressor, respectively, suggesting that the proline-P5C metabolic axis is a key checkpoint for tumor cell growth. Here, we report a metabolic reprogramming of 3D tumor cell growth by oncogenic Kaposi’s sarcoma-associated herpesvirus (KSHV), an etiological agent of Kaposi’s sarcoma and primary effusion lymphoma. Metabolomic analyses revealed that KSHV infection increased nonessential amino acid metabolites, specifically proline, in 3D culture, not in 2D culture. Strikingly, the KSHV K1 oncoprotein interacted with and activated PYCR enzyme, increasing intracellular proline concentration. Consequently, the K1-PYCR interaction promoted tumor cell growth in 3D spheroid culture and tumorigenesis in nude mice. In contrast, depletion of PYCR expression markedly abrogated K1-induced tumor cell growth in 3D culture, not in 2D culture. This study demonstrates that an increase of proline biosynthesis induced by K1-PYCR interaction is critical for KSHV-mediated transformation in in vitro 3D culture condition and in vivo tumorigenesis. [ABSTRACT FROM AUTHOR]

UV-induced cell pigmentation represents an important mechanism against skin cancers. Sun-exposed skin secretes α-MSH, which induces the lineage-specific transcriptional factor MITF and activates melanogenesis in melanocytes. Here, we show that the autophagic tumor suppressor UVRAG plays an integral role in melanogenesis by interaction with the biogenesis of lysosome-related organelles complex 1 (BLOC-1). This interaction is required for BLOC-1 stability and for BLOC-1-mediated cargo sorting and delivery to melanosomes. Absence of UVRAG dispersed BLOC-1 distribution and activity, resulting in impaired melanogenesis in vitro and defective melanocyte development in zebrafish in vivo. Furthermore, our results establish UVRAG as an important effector for melanocytes' response to α-MSH signaling as a direct target of MITF and reveal the molecular basis underlying the association between oncogenic BRAF and compromised UV protection in melanoma. [ABSTRACT FROM AUTHOR]