title: Optimization of energy-consuming pathways towards rapid growth in HPV-transformed cells.
abstract: Cancer is a complex, multi-step process characterized by misregulated signal transduction and altered metabolism. Cancer cells divide faster than normal cells and their growth rates have been reported to correlate with increased metabolic flux during cell transformation. Here we report on progressive changes in essential elements of the biochemical network, in an in vitro model of transformation, consisting of primary human keratinocytes, human keratinocytes immortalized by human papillomavirus 16 (HPV16) and passaged repeatedly in vitro, and the extensively-passaged cells subsequently treated with the carcinogen benzo[a]pyrene. We monitored changes in cell growth, cell size and energy metabolism. The more transformed cells were smaller and divided faster, but the cellular energy flux was unchanged. During cell transformation the protein synthesis network contracted, as shown by the reduction in key cap-dependent translation factors. Moreover, there was a progressive shift towards internal ribosome entry site (IRES)-dependent translation. The switch from cap to IRES-dependent translation correlated with progressive activation of c-Src, an activator of AMP-activated protein kinase (AMPK), which controls energy-consuming processes, including protein translation. As cellular protein synthesis is a major energy-consuming process, we propose that the reduction in cell size and protein amount provide energy required for cell survival and proliferation. The cap to IRES-dependent switch seems to be part of a gradual optimization of energy-consuming mechanisms that redirects cellular processes to enhance cell growth, in the course of transformation.
authors.affiliation: Unit of Cellular Signaling, Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Sarit
authors.initials: S
authors.lastname: Mizrachy-Schwartz
authors.forename: Nataly
authors.initials: N
authors.lastname: Kravchenko-Balasha
authors.forename: Hannah
authors.initials: H
authors.lastname: Ben-Bassat
authors.forename: Shoshana
authors.initials: S
authors.lastname: Klein
authors.forename: Alexander
authors.initials: A
authors.lastname: Levitzki
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D001564:Benzo(a)pyrene / Q000633:toxicity; D000081247:CSK Tyrosine-Protein Kinase; D002273:Carcinogens / Q000633:toxicity; D002455:Cell Division / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004789:Enzyme Activation; D052162:Human papillomavirus 16 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology* / Q000821:virology; D008751:Methylene Blue; D009369:Neoplasms / Q000473:pathology; D010101:Oxygen Consumption / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D019061:src-Family Kinases
chemical_list: D002273:Carcinogens; D001564:Benzo(a)pyrene; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D000263:Adenylate Kinase; D008751:Methylene Blue