Int-2, an autocrine and/or ultra-short-range effector in transgenic mammary tissue transplants.
BACKGROUND
Previous studies have shown associations between overexpression of int-2 messenger RNA (mRNA) and murine mammary tumors and between amplification of the int-2 genomic locus and human breast cancers. The Int-2 protein (fibroblast growth factor 3) is a member of the heparin-binding growth factor family of proteins. The export of these growth factors from cells may depend on the presence of amino terminal sequences containing hydrophobic signal peptides. Although Int-2 has a putative signal sequence, it is not known whether or how this protein is secreted from cells.


OBJECTIVE
Assuming that the Int-2 protein is secreted from mammary epithelial cells in a basolateral direction so that it is available to affect adjacent cells, we investigated whether it acts in a paracrine manner, exerting its effect externally on adjacent cells, or in an autocrine manner, exerting its effect internally within the same cell.


METHODS
Using in situ hybridization with 35S-labeled RNA antisense probes that specifically detect mRNA coding for the Int-2 protein, we determined the cell-specific localization of int-2 mRNA expression in the mammary gland of transgenic FVB/N mice overexpressing int-2 mRNA. Then we transplanted pieces of mammary epithelial tissue expressing int-2 mRNA into the mammary fat-pad of wild-type, syngeneic animals. The mammary glands of host animals were examined as whole-mounts and as histologic sections 2-6 months after transplantation. In situ hybridization was used to confirm which cells continued to express int-2 mRNA following transplantation.


RESULTS
Int-2 mRNA expression in transgenic mice was localized to the mammary epithelial cells. Transplants expressing int-2 mRNA were similar to wild-type transplants in that they had no observable effect on either the growth or the morphology of host mammary epithelium. Abnormal growth occurred only in transplanted tissue expressing int-2 mRNA but not in adjacent host mammary epithelium.


CONCLUSIONS
Given the limitations of our experimental system and the limited information available to date on the secretion of Int-2 protein, these results suggest that, although the Int-2 protein contains a putative signal peptide, it may act primarily as an autocrine or as an ultra-short-range paracrine growth factor in mammary epithelium.
Ornitz
D M
DM
Howard Hughes Medical Institute, Harvard Medical School, Boston, Mass.
Cardiff
R D
RD
Kuo
A
A
Leder
P
P
D000818:Animals; D016375:Antisense Elements (Genetics); D001345:Autoradiography; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics; D004848:Epithelium / Q000502:physiology; D005260:Female; D051518:Fibroblast Growth Factor 3; D005346:Fibroblast Growth Factors; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics; D006801:Humans; D008321:Mammary Glands, Animal / Q000166:cytology / Q000502:physiology* / Q000637:transplantation; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D051379:Mice; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D009693:Nucleic Acid Hybridization; D011247:Pregnancy; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000502:physiology; D015347:RNA Probes; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000032:analysis; D029701:Saccharomyces cerevisiae Proteins; D013462:Sulfur Radioisotopes; D014157:Transcription Factors; D014185:Transplantation, Isogeneic
D016375:Antisense Elements (Genetics); D004268:DNA-Binding Proteins; C496444:FGF3 protein, human; C489197:Fgf3 protein, mouse; D051518:Fibroblast Growth Factor 3; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D021382:Protein Sorting Signals; D011518:Proto-Oncogene Proteins; D015347:RNA Probes; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D013462:Sulfur Radioisotopes; D014157:Transcription Factors; D005346:Fibroblast Growth Factors; D011505:Protein-Tyrosine Kinases