Biomedical subjects

Harold Kim

Publications and source records attributed to Harold Kim.

4 recordsLinked to original sources

PubMed2002

Correlating structural dynamics and function in single ribozyme molecules.

We have studied the correlation between structural dynamics and function of the hairpin ribozyme. The enzyme-substrate complex exists in either docked (active) or undocked (inactive) conformations. Using single-molecule fluorescence methods, we found complex structural dynamics with four docked states of distinct stabilities and a strong memory effect where each molecule rarely switches between different docked states. We also found substrate cleavage to be rate-limited by a combination of conformational transitions and reversible chemistry equilibrium. The complex structural dynamics quantitatively explain the heterogeneous cleavage kinetics common to many catalytic RNAs. The intimate coupling of structural dynamics and function is likely a general phenomenon for RNA.

Carbocyanines↗

PubMed2002

The effects of exogenous p53 overexpression on HPV-immortalized and carcinogen transformed oral keratinocytes.

BACKGROUND: Overexpression of p53 in head and neck carcinoma cells has demonstrated tumor growth suppression using in vitro and in vivo models. The effects of exogenous overexpression of wild-type p53 on human papilloma virus (HPV)-immortalized and carcinogen transformed oral keratinocytes were determined. METHODS: The p53 gene was overexpressed in IHGK (immortalized human gingival keratinocyte), IHGKN [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, (NNK)]-carcinogen transformed keratinocytes, and two head and neck squamous carcinoma (HNSCC) cell lines, HN30 and HN12. The transfection efficiency, growth suppression, and inhibition of the cell cycle along with the induction of apoptosis were measured. RESULTS: Transfections with adenoviruses were more efficient for IHGK cells than for IHGKN, HN12, and HN30 cells. Inhibition of proliferation in all cell lines was proportional to the viral particle to cell (VPC) ratios. IHGK cells were more sensitive to p53 than IHGKN cells. HN12 cells were more suppressed than HN30 cells. HN12 were the most suppressed at 72 hours whereas HN30 cells were most suppressed at 24 hours. Expression of exogenous p53-induced G1 cell cycle arrest and p21 expression as VPC ratios increased in IHGK and IHGKN cell lines. Apoptosis also was induced in these cells by p53 as VPC increased. IHGK cells were more sensitive to p53-induced growth inhibition, cell cycle regulation, p21 expression and apoptosis than IHGKN cells. HN12 (mutated p53) cells were more sensitive to p53 overexpression than HN30 (wild-type p53) cells. Gene transfer and expression of exogenous p53 by using Ad-p53 demonstrates suppressive effects on HPV immortalized and carcinogen transformed oral keratinocytes. CONCLUSIONS: Cell cycle regulation by gene transfer is feasible in immortalized oral keratinocytes. Carcinogen transformed cells are less susceptible to the effects of p53 overexpression. Expression of exogenous p53 through p53 gene transfer can suppress HPV immortalization and carcinogen transformation in oral keratinocytes. The sensitivity of HNSCC cell lines to p53-induced cell cycle regulation and apoptosis is variable and dependent on the cell line and duration of exposure. In vitro results using p53 gene transfer must be validated in clinical studies with patients at risk for HNSCC.

Adenoviridae↗

PubMed2002

In vivo characteristics of HPV-immortalized and carcinogen transformed oral keratinocytes.

PURPOSE: To characterize in vivo features of HPV-immortalized and carcinogen transformed oral keratinocytes. METHODS: The growth and squamous differentiation of IHGK (immortalized human gingival keratinocyte with HPV), IHGKN [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, (NNK)]-carcinogen transformed keratinocytes, and two head and neck squamous cell carcinoma (HNSCC) cell lines, HN30 and HN12, were tested by injecting these cells into SCID mice. The growth, histological features, and expression of PCNA, Involucrin, and high molecular weight keratin of the tumors formed were compared among these cell lines. RESULTS: All cell lines formed a palpable lesion at 2 weeks; however, only HN30 continued to grow. IHGK and IHGKN cells formed palpable nodules within 2 weeks with no further growth after 4 to 5 weeks, and no regression of the nodule was noted at 12 weeks. HN12 cells did not form tumor nodules unless these cells were co-injected with immortalized fibroblasts. Both IHGK and IHGKN cells formed a well-circumscribed epithelial lesion with islands of differentiated squamous cells bound by a myxoid matrix. Nests of basal-horny squamous cells centrally differentiated into anucleate squamous cells. IHGK and IHGKN nodules had more squamous differentiation than HN12 and HN30 and further differentiated over time. IHGK and IHGKN cells expressed differentiation (involucrin and high molecular weight keratin) and proliferation (PCNA) markers that suggest that IHGK and IHGKN behave as well-differentiated squamous lesions when compared with malignant HN12 and HN30 nodules. IHGK and IHGKN cells showed an initial growth phase followed by terminal differentiation, and then a phase characterized by regression and host inflammatory stage. CONCLUSIONS: The growth, histology, and expression of differentiation and proliferation markers of IHGK and IHGKN lesions into SCID mice demonstrate that these cells are endowed with a limited malignant potential. Our in vivo model with these intermediate cell lines can provide a short-term analysis for studying the biology of HNSCC progression and the activity of chemoprevention agents.

Animals↗

PubMed2002

Anticancer activity of docetaxel in murine salivary gland carcinoma.

PURPOSE: The purpose of this study was to evaluate the biological mechanisms of docetaxel (TXT) on salivary gland carcinoma. EXPERIMENTAL DESIGN: The effects of TXT on a spontaneous murine salivary carcinoma were determined. Proliferation, cell cycle regulation, connexin43 expression, gap-junctional intercellular communication, apoptosis, and Fas receptor (FasR) expression were measured. RESULTS: We characterized a spontaneous mouse salivary gland carcinoma (SGC1). SGC1 is a poorly differentiated carcinoma that originated from the parotid gland of a BALB/c mouse. SGC1 cells were cultured and found to be immortal past 30 passages. Initially, cells formed tumor nodules in severe combined immunodeficient (SCID) mice. Afterward, SGC1 cells that were subcultured from SCID tumors readily formed colonies in soft agar and were highly tumorigenic in SCID mice and immune-competent BALB/c hosts. Dose response for TXT with respect to growth suppression, G(2)-M cell cycle arrest, and apoptosis was found. Induction of apoptosis by TXT coincided with an increase in cell surface FasR expression. Up-regulation of FasR with lower doses of TXT rendered cells susceptible to FasR agonist antibody-mediated apoptosis. In the absence of TXT, anti-FasR antibodies were completely without effect, suggesting that TXT is critical for priming apoptosis mediated through the Fas pathway. In addition, gap-junctional intercellular communication was augmented by TXT in SGC1 cells concomitant with increased connexin43 expression and membrane localization. CONCLUSIONS: We have identified several novel targets of TXT that contribute to its antitumor activity in poorly differentiated salivary gland carcinoma. These results suggest that TXT may be appropriate for additional in vivo studies and clinical trials in patients with salivary cancers.

Adenocarcinoma↗