Our Science – Kasprzak Website

Kazimierz S. Kasprzak, Ph.D., D.Sc.

Laboratory of Comparative Carcinogenesis Scientist Emeritus Building 538, Room 205E NCI-Frederick Frederick, MD 21702-1201 Phone:   301-846-5738 Fax:   301-846-5946 E-Mail:   kasprkaz@ncifcrf.gov

Biography

Dr. Kasprzak received his M.S. and Ph.D. in chemistry from the University of Poznan, and his D.Sc. in metal toxicology from the University Medical School of Poznan, Poland. He held several positions at academic medical schools in Poland and the United States, and served in the International Union of Pure and Applied Chemistry Divisions of Clinical and Analytical Chemistry. He joined the NIH in 1982 to study the carcinogenicity of metals.

Research

Mechanisms of Transition Metal-Induced Carcinogenesis

Certain transition metals, including nickel, chromium, cadmium, and copper, are carcinogenic to humans and/or animals. They may induce occupational lung cancer in metallurgy workers and childhood neoplasia in their progeny. However, mechanisms of the carcinogenic activity of these metals remain obscure. In recent years, we have been testing a hypothesis that one such mechanism would involve metal-mediated oxidative damage to DNA and nuclear proteins. Our investigations are focused on transition metals' interactions with protamines, histones, and selected antimutagenic and tumor suppressor enzymes, phosphohydrolases. More recently, we also initiated research based on another hypothesis that the carcinogenic action of metals would include induction of the hypoxic response in cells. This research is centered around metals' effects on the hypoxia-inducible factor HIF-1-alpha.


The results of our investigations of protamine HP2 allowed us to propose two physiological binding sites for Zn(II) in the sperm chromatin. These binding sites were different from the N terminal site found for Ni(II) and Cu(II). Toxicity of the latter metals has been associated with redox catalysis. Ni(II) and Cu(II) coordinated by the N terminal Arg-Thr-His- motif of HP2 are redox active and mediate oxidative damage to the peptide, the major target for oxidation being Tyr-8. A 2D NMR study has revealed that the reason for this specificity is strong structuring effect of the N-terminally coordinated Ni(II) on the rest of the molecule that brings Tyr-8 close to the metal center. Interactions of this kind may be responsible for sperm chromatin damage and, possibly, for childhood cancer in the progeny of metal workers.


Using synthetic model peptides, we investigated Ni(II) interactions with the core histones. The formation of a strong complex with the TESHHK end motif in the C terminal tail of histone H2A and hydrolysis of this motif by Ni(II) between the glutamic acid and serine residues were found in peptides of various lengths modeling the tail, and in whole bovine H2A. The secondary complex formed between Ni(II) and the cut-off SHHKAKGK product of H2A hydrolysis is redox-active and is capable of enhancing oxidative promutagenic damage to DNA. More recently, we have confirmed the truncation in cells cultured in Ni(II)-containing media. In addition, the same cells showed truncation and other modifications (e.g., ubiquitinylation and deamidation) of yet another core histone, histone H2B. Since the physiological roles of the histone tails include locking interactions with other histones and DNA, the observed effects may alter chromatin structure and gene expression pattern, as observed in nickel-exposed cells.


The investigations of phosphohydrolases have been focused on MTH1 protein, an 8-oxo-dGTPase, preventing incorporation of promutagenic 8-oxo-dGTP into DNA, and on Fhit, a tumor suppressor protein having diadenosine triphosphate (Ap₃A) phosphohydrolytic activity. We confirmed the inhibition of MTH1 activity by Cd(II) in the testes of rats exposed to Cd(II), the rat testicular carcinogen. Immunohistochemical staining revealed for the first time presence of MTH1 in cell nuclei and in the acrosomic vesicles of spermatocytes and sperm. Possible inhibition of MTH1 in the sperm may be relevant to preconception carcinogenesis. Several metals, Cu(II)>>Ni(II)>Zn(II)>Cr(III)>Cd(II)>>Co(II), were found to inhibit recombinant human Fhit with efficiency decreasing in the given ranking. The exceptionally high inhibitory potential of Cu(II) (IC₅₀ = 0.4 microM) is apparently due to oxidation by Cu(II) of the Cys-39 with resulting dimerization of Fhit molecule through –S–S– bond. Also, Fhit expression was found to be significantly lower, or even absent, in nickel-exposed cells and in nickel-induced mouse sarcomas. Thus, both MTH1 and Fhit may participate in the mechanisms of metal-induced mutagenesis and carcinogenesis.

Our research on the mechanisms of hypoxia-mimicking effects of Ni(II), Co(II), and Cr(VI) revealed thus far a critical contribution of cellular ascorbate depletion by these metals to the observed inhibition of prolyl hydroxylase and activation of HIF-1-alpha. Such activation my be averted by ascorbic acid supplementation that bears a potential practical importance for the development of prevention strategies against lung cancer in metal industries. The prevention is being investigated with the use of Gulo-/- knock-out mice that, like humans, have no endogenous synthesis of ascorbic acid.

Extramural collaborators on this research are: Wojciech Bal, Polish Academy of Sciences, Warsaw, Poland; Malgorzata Jezowska-Bojczuk, University of Wroclaw, Poland; Miral Dizdaroglu, National Institute of Standards and Technology, Gaithersburg, MD; Anatoly Zhitkovich, Brown University, Providence, RI; and Yusaku Nakabeppu, Kyushu University, Japan.

This page was last updated on 3/25/2008.