Exosomes in colorectal carcinoma formation: ALIX under the magnifying glass

Mod Pathol. 2016 Aug;29(8):928-38. doi: 10.1038/modpathol.2016.72. Epub 2016 May 6.

Abstract

Exosomes are small membrane vesicles that have important roles in transporting a great variety of bioactive molecules between epithelial compartment and their microenvironment during tumor formation including colorectal adenoma-carcinoma sequence. We tested the mRNA expression of the top 25 exosome-related markers based on ExoCharta database in healthy (n=49), adenoma (n=49) and colorectal carcinoma (n=49) patients using Affymetrix HGU133 Plus2.0 microarrays. Most related genes showed significantly elevated expression including PGK1, PKM, ANXA5, ENO1, HSP90AB1 and MSN during adenoma-carcinoma sequence. Surprisingly, the expression of ALIX (ALG 2-interacting protein X), involved in multivesicular body (MVB) and exosome formation, was significantly reduced in normal vs adenoma (P=5.02 × 10(-13)) and in normal vs colorectal carcinoma comparisons (P=1.51 × 10(-10)). ALIX also showed significant reduction (P<0.05) at the in situ protein level in the epithelial compartment of adenoma (n=35) and colorectal carcinoma (n=37) patients compared with 27 healthy individuals. Furthermore, significantly reduced ALIX protein levels were accompanied by their gradual transition from diffuse cytoplasmic expression to granular signals, which fell into the 0.6-2 μm diameter size range of MVBs. These ALIX-positive particles were seen in the tumor nests, including tumor-stroma border, which suggest their exosome function. MVB-like structures were also detected in tumor microenvironment including α-smooth muscle actin-positive stromal cells, budding off cancer cells in the tumor front as well as in cancer cells entrapped within lymphoid vessels. In conclusion, we determined the top aberrantly expressed exosome-associated markers and revealed the transition of diffuse ALIX protein signals into a MVB-like pattern during adenoma-carcinoma sequence. These tumor-associated particles seen both in the carcinoma and the surrounding microenvironment can potentially mediate epithelial-stromal interactions involved in the regulation of tumor growth, metastatic invasion and therapy response.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoma / chemistry*
  • Adenoma / genetics
  • Adenoma / pathology
  • Aged
  • Aged, 80 and over
  • Biomarkers, Tumor / analysis*
  • Biomarkers, Tumor / genetics
  • Calcium-Binding Proteins / analysis*
  • Calcium-Binding Proteins / genetics
  • Carcinoma / chemistry*
  • Carcinoma / genetics
  • Carcinoma / pathology
  • Case-Control Studies
  • Cell Cycle Proteins / analysis*
  • Cell Cycle Proteins / genetics
  • Colorectal Neoplasms / chemistry*
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • Endosomal Sorting Complexes Required for Transport / analysis*
  • Endosomal Sorting Complexes Required for Transport / genetics
  • Exosomes / chemistry*
  • Exosomes / genetics
  • Exosomes / pathology
  • Female
  • Gene Expression Profiling / methods
  • Humans
  • Immunohistochemistry
  • Male
  • Middle Aged
  • Multivesicular Bodies / chemistry*
  • Multivesicular Bodies / genetics
  • Multivesicular Bodies / pathology
  • Oligonucleotide Array Sequence Analysis
  • Tumor Microenvironment

Substances

  • Biomarkers, Tumor
  • Calcium-Binding Proteins
  • Cell Cycle Proteins
  • Endosomal Sorting Complexes Required for Transport
  • PDCD6IP protein, human