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We constructed an adenoviral vector containing human p16 cDNA in order to evaluate the cytotoxic eects of exogenous p16 expression on cancer cell proliferation and to explore the potential use of p16 in cancer gene therapy. Following infection of human breast (MCF-7, MDA-MB-231, and BT549), osteosarcoma (U-2 OS and Saos-2), cervical (C33a), and lung cancer (H358) cell lines with the recombinant adenovirus Adp16, high levels of p16 expression were observed in all cell lines. Cancer cell lines which were mutant or null for p16 but wild-type for the retinoblastoma gene product (pRb) (MCF-7, MDA-MB-231, BT549 and U-2 OS) were 7 ± 22-fold more sensitive to the cytotoxic eects of Adp16 than to a control virus. In contrast, cancer cell lines which were wild-type for p16 but mutant or null for pRb (Saos-2, C33a and H358) were 5threefold more sensitive to Adp16 when compared to a control virus. Analysis of 5-bromodeoxyuridine incorporation into DNA following infection with Adp16 showed a loss of S phase in those cell lines which were null or mutant for p16 but expressed a functional pRb. This cell cycle arrest was associated with binding of the p16 protein to cyclindependent kinase 4 and dephosphorylation of pRb. In contrast, human cancer cell lines expressing a wild-type p16 and a mutant pRb or no pRb showed no substantial loss of S phase following Adp16 infection. Based on these studies, we conclude that p16-mediated cytotoxicity is tightly associated with the presence of functional pRb in human cancer cells, and that tumor cells which are mutant or null for p16 are candidates for Adp16 mediated cancer gene therapy.

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Chronic hypoxia increased myocardial tolerance to ischaemia, and acute ischaemic preconditioning increased the tolerance further. Thus chronic hypoxia and acute ischaemic preconditioning independently activate protective mechanisms against ischaemia; the mechanisms may differ between the two types of insult.

To study the molecular basis of vascular remodeling in pulmonary hypertension, we developed an experimental system in which male Sprague-Dawley rats were exposed to hypoxia for up to 3 wk. Both the right ventricular systolic pressure and gravimetric index for right ventricular hypertrophy were higher in rats exposed to hypoxia for 3 wk than those of age-matched control rats (P < 0.01), indicating that pulmonary hypertension was established under conditions used. To examine the possible involvement of platelet-derived growth factor (PDGF) in the pulmonary vascular remodeling caused by hypoxia, we cloned rat PDGF A- and B-chain cDNA and prepared specific cRNA probes. Northern blot analysis revealed that PDGF B-chain mRNA levels in the lungs were increased, reached a maximum of day 1, and were sustained at day 3, whereas PDGF A-chain mRNA levels reached a maximum on day 3. Thus the increase in the PDGF B-chain mRNA level precedes that in the PDGF A-chain mRNA level. These results suggest that the PDGF A- and B-chain products may be coordinately and sequentially involved in hypoxic pulmonary vascular remodeling.

In mammals, histamine is inactivated principally by two enzymes: histamine N-methyltransferase (HMT; EC 2.1.1.8) and diamine oxidase (DAO; EC 1.4.3.6.). The cDNA clone of human HMT (hHMT) has been isolated from a cDNA library of human kidney and its nucleotide, and deduced amino acid sequences have been determined. One clone, phHMT-1, containing an insert of 1.4 kb, was confirmed to encode HMT by transient expression of HMT activity in COS cells. hHMT consists of 292 amino acid residues [relative molecular weight (M(r)) = 33,279] and shares 82% identity with that of rat HMT. Northern blot analysis with hHMT cDNA probe revealed that 1.6-kb HMT mRNA transcript was expressed in the lung, nasal polyps, and kidney. HMT activity was measured in human trachea and bronchi. In addition, the contractile response of isolated human bronchi to histamine was potentiated in the presence of an HMT inhibitor, SKF 91488, but a DAO inhibitor, aminoguanidine, was without effect. These results suggest that HMT plays an important role in degrading histamine and in regulating the airway response to histamine. Therefore, the level of HMT gene expression in human airway may be one of the critical factors determining the airway responsiveness to histamine. In situ chromosomal hybridization demonstrated that human HMT gene was localized in chromosome 1 p32.

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