Human renal clear cell carcinoma (RCC) is frequently associated with loss of the von Hippel-Lindau (VHL)tumor suppressor (pVHL), which inhibits ubiquitylation and degradation of the alpha subunits of hypoxiainducible transcription factor. pVHL also ubiquitylates the large subunit of RNA polymerase II, Rpb1, phosphorylated on serine 5 (Ser5) within the C-terminal domain (CTD). A hydroxylated proline 1465 within an LXXLAP motif located N-terminal to the CTD allows the interaction of Rpb1 with pVHL. Here we report that in RCC cells, pVHL regulates expression of Rpb1 and is necessary for low-grade oxidative-stress-induced recruitment of Rpb1 to the DNA-engaged fraction and for its P1465 hydroxylation, phosphorylation, and nondegradative ubiquitylation. Egln-9-type prolyl hydroxylases, PHD1 and PHD2, coimmunoprecipitated with Rpb1 in the chromatin fraction of VHL ؉ RCC cells in response to oxidative stress, and PHD1 was necessary for P1465 hydroxylation while PHD2 had an inhibitory effect. P1465 hydroxylation was required for oxidativestress-induced Ser5 phosphorylation of Rpb1. Importantly, overexpression of wild-type Rpb1 stimulated formation of kidney tumors by VHL ؉ cells, and this effect was abolished by P1465A mutation of Rpb1. These data indicate that through this novel pathway involving P1465 hydroxylation and Ser5 phosphorylation of Rbp1, pVHL may regulate tumor growth.pVHL is the main tumor suppressor for which loss of activity is causatively linked to renal clear cell carcinoma (RCC), the most malignant and common form of kidney cancer. The VHL gene is mutated or hypermethylated in about 40 to 70% of sporadic RCC. Hereditary loss of pVHL function in von Hippel-Lindau (VHL) disease also results in highly vascularized RCC and capillary tumors of other organs, such as hemangioblastoma of the central nervous system and retinal angioma (19,20). A body of experimental evidence, based on a subcutaneous xenograft model system, supports the idea that accumulation of the alpha subunit of the hypoxia-inducible transcription factor (HIF) HIF-2␣ and induction of HIF target gene products, resulting from the loss of pVHL-mediated ubiquitylation, are necessary and sufficient to promote growth of RCC tumors (22,23). HIF activation has also been demonstrated as an early tumorigenesis event in kidneys from VHL patients (32). Biochemically, pVHL is the substrate-recognizing component of a multiprotein E3 ubiquitin ligase complex containing elongins C and B, Cullin 2, and the RING-H2 finger protein Rbx-1 (for a review, see reference 19). pVHL-dependent ubiquitylation of HIF-␣s is preceded by hydroxylation of conserved proline residues located within LXXLAP motifs (16,17) by the O 2 -, Fe(II)-, and oxyglutarate-regulated Egl-9-type proline hydroxylases (PHDs) (7). Thus, an important aspect of pVHL's tumor suppressing activity is the prevention of HIF-␣ accumulation, which in turn suppresses induction of the HIF target genes. Clearly, however, pVHL activity is not limited to regulation of HIFs. Other targets of pVHL-associated E...

Propionyl-CoA carboxylase [PCC, propan-oyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.3] is a biotin-dependent enzyme involved in the degradation of branched-chain amino acids, fatty acids with odd-numbered chain lengths, and other metabolites. Inherited deficiency of the enzyme results in propionic acidemia, an autosomal recessive disorder showing considerable clinical heterogeneity. To facilitate investigations of enzyme structure and the nature of mutation in propionic acidemia, we have isolated cDNA clones coding for the a and P polypeptides of human PCC. Sequences of two peptides derived from human liver PCC were used to specify oligonucleotide probes that were then used to screen a human fibroblast cDNA library. Two classes of cDNA clones were thus identified. One class contained the anticipated Ala-Met-Lys-Met sequence, corresponding to the biotin bind. ing site found in several biotin-dependent carboxylases, thus confirming the a-chain assignment of these clones. In addition, they contained the deduced amino acid sequence of two of the sequenced peptides, incuding that of one of the oligonucleotide probes. The second class, coding for the (3 polypeptide, contained the sequences of four peptides, including the sequence corresponding to the other oligonudeotide probe. Blot hybridization of RNA from normal human fibroblasts revealed a single mRNA species of 2.9 kilobases coding for the a polypeptide and two species of 4.5 and 2.0 kilobases detected for the ( polypeptide. By use of a panel of somatic mouse-human hybrids, the human gene encoding the a polypeptide (PCCA) was localized to chromosome 13, while the gene encoding the ( polypeptide (PCCB) was assigned to chromosome 3. Restriction fragment length polymorphisms were identified, at both PCCA and PCCB, that should prove useful to individual families at risk for propionic acidemia.

A. BAIRD? A-M. GONZALEZ? E. FLORKIEWICZ, 109 FIGURE 1. Comparative northern and immunoblot analysis of TE671 and SK-Hep-1 cells. Top panel: 20 pg of total RNA from both cell lines was fractionated on formaldehyde-agarose gels, transferred to nitrocellulose, and hybridized with I2P-labeled human bFGF cDNA probe, lanes 1 and 2; or beta-actin probe, lanes 3 and 4. SK-Hep-1 and TE671 RNA are shown in lanes 1 and 3, and lanes 2 and 4, respectively. Bottom panel: Immunoblot analysis of heparin-Sepharose purified proteins from TE671 (lane 1) and SK-Hep-1 (lane 3) cells. Blots were probed with guinea pig anti-bFGF (18-kDa) antibody and '"I-protein A. Signal is visualized by autoradiography. Lane 2, human recombinant bFGF (5 ng) size marker. Arrows mark the location of three bFGF specific immunoreactive bands as has been previously described? Molecular weight standards are shown in kilodaltons.

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