590 demarcated from the surrounding tissue. If indeed MMP-2 activity is essential to hepatocyte migration, then its low expression within nodular hepatocytes might help in explaining their inability to crawl in between surrounding hepatocytes and their lack of integration into the host liver, thereby giving rise to proliferative focal lesions. In summary, the present study compares the fate of nor- mal and nodular hepatocytes following orthotopic trans- plantation into syngeneic host liver pre-conditioned with RS. Both cell types underwent selective clonal expansion, as expected, indicating that growth per se was not a distin- guishing feature between the two cell populations. However, their growth pattern and biological fates were remarkably different, and this was associated with altered expression of DPPIV, Cx32, E-cadherin, and MMP-2 proteins, markers associated with cell polarity, cell-to-cell communication, cell adhesion, and cell migration. We interpret these ﬁndings as supporting the concept of a dominant biological pathway leading to neoplastic disease involving defect(s) in tissue pattern formation (Feigin and Muthuswamy 2009; Wang 2009; Wodarz and Na¨thke 2007). Several molecular alter- ations, other than the ones described in these studies, are likely to result in a similar phenotype. Acknowledgments This work was supported by AIRC (Italian Association for Cancer Research, grant No. 4927 and 10604 to EL). We thank Anna Saba and Giovanna Porqueddu for their excellent technical and secretarial assistance. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References Archer KJ, Mas VR, David K, Maluf DG, Bornstein K, Fisher RA (2009) Identifying genes for establishing a multigenic test for hepatocellular carcinoma surveillance in hepatitis C virus- positive cirrhotic patients. Cancer Epidemiol Biomarkers Prev 18:2929–2932 Cai L, Mostov K (2009) Polarity is destiny. Cell 139:660–662 Chen A, Cuevas I, Kenny PA, Miyake H, Mace K, Ghajar C, Boudreau A, Bissell M, Boudreau N (2009) Endothelial cell migration and vascular endothelial growth factor expression are the result of loss of breast tissue polarity. Cancer Res 69: 6721–6729 Clark WR Jr, Elder DE, Guerry D 4th, Epstein MN, Greene MH, Van Horn M (1984) A study of tumor progression: the precursor lesions of superﬁcial spreading and nodular melanoma. Hum Pathol 15:1147–1165 Diallo R, Schaefer KL, Poremba C, Shivazi N, Willmann V, Buerger H, Dockhorn-Dworniczak B, Boecker W (2001) Monoclonality in normal epithelium and in hyperplastic and neoplastic lesions of the breast. J Pathol 193:27–32 Doratiotto S, Marongiu F, Faedda S, Pani P, Laconi E (2009) Altered growth pattern, not altered growth per se, is the hallmark of early 123 Histochem Cell Biol (2011) 135:581–591 lesions preceding cancer development. Histol Histopathol 24: 101–106 Ellerbroek SM, Stack MS (1999) Membrane associated matrix metalloproteinases in metastasis. Bioessays 21:940–949 Feigin ME, Muthuswamy SK (2009) Polarity proteins regulate mammalian cell-cell junctions and cancer pathogenesis. Curr Opin Cell Biol 21:694–700 Foulds L (1975) Neoplastic Development, vol 2. Academic Press, New York, pp 1–15 Fridman R, Toth M, Pen˜a D, Mobashery S (2009) Activation of progelatinase B (MMP-9) by gelatinase A (MMP-2). Cancer Res 55:2548–2555 Garcia SB, Novelli M, Wright (2000) The clonal origin and clonal evolution of epithelial tumours. Int J Exp Pathol 81:89–116 Hanahan D, Weinberg RA (2000) The hallmarks of cancer. Cell 100:57–70 Hruban RH, Goggins M, Parsons J, Kern SE (2000) Progression model for pancreatic cancer. Clin Cancer Res 6:2969–2972 Hytiroglou P, Park Y, Krinsky G, Theise ND (2007) Hepatic precancerous lesions and small hepatocellular carcinoma. Gas- troenterol Clin North Am 36:867–887 Iannaccone PM, Weinberg WC, Deamant FD (1987) On the clonal origin of tumors: a review of experimental models. Int J Cancer 39:778–784 Ihara A, Koizumi H, Hashizume R, Uchikoshi T (1996) Expression of epithelial cadherin and alpha- and beta-catenins in nontumoral livers and hepatocellular carcinomas. Hepatology 23:1441–1447 Koenig S, Stoesser C, Krause P, Becker H, Markus PM (2005) Liver repopulation after hepatocellular transplantation: integration and interaction of transplanted hepatocytes in the host. Cell Trans- plant 14:31–40 Kon J, Ichinohe N, Ooe H, Chen Q, Sasaki K, Mitaka T (2009) Thy1- positive cells have bipotential ability to differentiate into hepatocytes and biliary epithelial cells in galactosamine-induced rat liver regeneration. Am J Pathol 175:2362–2371 Kren BT, Kumar NM, Wang SQ, Gilula NB, Steer CJ (1993) Differential regulation of multiple gap junction transcripts and proteins during rat liver regeneration. J Cell Biol 123:707–718 Krutovskikh VA, Oyamada M, Yamasaki H (1991) Sequential changes of gap-junctional intercellular communications during multistage rat liver carcinogenesis: direct measurement of communication in vivo. Carcinogenesis 12:1701–1706 Laconi S, Laconi E (2002) Principles of hepatocyte transplantation. Semin Cell Dev Biol 13:433–438 Laconi S, Curreli F, Diana S, Pasciu D, De Filippo G, Sarma DSR, Pani P, Laconi E (1999) Liver regeneration in response to partial hepatectomy in rats treated with retrorsine: a kinetic study. J Hepatol 31:1069–1074 Laconi S, Pani P, Pillai S, Pasciu D, Sarma DSR, Laconi E (2001a) A growth constrained environment drives tumor progression in vivo. Proc Natl Acad Sci USA 98:7806–7811 Laconi S, Pillai S, Porcu PP, Shafritz DA, Pani P, Laconi E (2001b) Massive liver replacement by transplanted hepatocytes in the absence of exogenous growth stimuli in rats treated with retrorsine. Am J Pathol 158:771–777 Lehti K, Lohi J, Valtanen H, Keski-Oja J (1998) Proteolytic processing of membrane-type-1 matrix metalloproteinase is associated with gelatinase A activation at the cell surface. Biochem J 334(Pt 2):345–353 Llovet JM, Chen Y, Wurmbach E, Roayaie S, Fiel MI, Schwartz M, Thung SN, Khitrov G, Zhang W, Villanueva A, Battiston C, Mazzaferro V, Bruix J, Waxman S, Friedman SL (2006) A molecular signature to discriminate dysplastic nodules from early hepatocellular carcinoma in HCV cirrhosis. Gastroenterol- ogy 131:1758–1767