Abstract 3999: Spontaneous time-dependent accumulation of interferon-regulatory factor 9 induces chemo-resistance in colon carcinoma cells independently of STAT1 signaling.
Authors: Kolosenko Iryna , Fryknäs Mårten , Rassoolzadeh Hanif , Pellegrini Paola , Brnjic Slavica , Johnsson Per , Di Lernia Giuseppe , Grander Dan , Larsson Rolf , Pokrovskaja Katja , Linder Stig , De Milito Angelo De Milito 
Published: August 2014

Abstract
Spontaneous time-dependent accumulation of interferon-regulatory factor 9 induces chemo-resistance in colon carcinoma cells independently of STAT1 signaling
Iryna Kolosenko1, Mårten Fryknäs2, Hanif Rassoolzadeh1, Paola Pellegrini1, Slavica Brnjic1, Per Johnsson1, Giuseppe Di Lernia1, Dan Grandér1, Rolf Larsson2, Katja Pokrovskaja Tamm1, Stig Linder1, Angelo De Milito1
1 Cancer Center Karolinska, Dep. Oncology-Pathology, Karolinska Institute, Stockholm, Sweden
2 Division of Clinical Pharmacology, Department of Medical Sciences, Uppsala University Hospital, 751 85 Uppsala, Sweden
Solid tumors contain microenvironments characterized by hypoxia and limited availability of nutrients. Such metabolically compromised environments show an increased level of resistance to many chemotherapeutic agents. Multicellular tumor spheroids (MCS) contain hypoxic and nutrient-starved cell populations and provide a model to study multicellular therapy-resistance. We here used 3D cultures of HCT116 colon cancer cells as a model to identify factors related to multicellular drug-resistance. Microarray analysis revealed a dramatic increase in the expression of interferon-alpha (IFNα)-regulated genes in the 3D as compared to 2D cultures. This finding is of significance since an IFNα-related gene signature has previously been associated with therapy resistance in several human cancers. IFNα is known to regulate gene transcription through transcription complex ISGF3 consisting of STAT1, STAT2 and IRF9, as well as through STAT1 homodimers. We found that IRF9, but not STAT1, was consistently induced in colon cancer cell lines grown in 3D as compared to the 2D cultures. Upregulation of IFN-induced genes was observed during crowding of monolayer HCT116 cultures, providing both mechanistic insight as well as a convenient experimental model. STAT1 knock-down experiments showed that induction of IRF9 occurred independently of STAT1. Interestingly, over-expression of IRF9 rendered monolayer 2D HCT116 cells significantly more resistant to cisplatin, docetaxel and etoposide. Vice versa, inhibition of IRF9 expression significantly increased drug-sensitivity of monolayer HCT116 cells to cisplatin. Our data further support an association of IFNα-related gene signature and drug resistance and suggest an important role for the STAT1-independent IRF9 upregulation associated with therapy resistance in cancer.
Citation Format: Iryna Kolosenko, Mårten Fryknäs, Hanif Rassoolzadeh, Paola Pellegrini, Slavica Brnjic, Per Johnsson, Giuseppe Di Lernia, Dan Grander, Rolf Larsson, Katja Pokrovskaja, Stig Linder, Angelo De Milito De Milito. Spontaneous time-dependent accumulation of interferon-regulatory factor 9 induces chemo-resistance in colon carcinoma cells independently of STAT1 signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3999. doi:10.1158/1538-7445.AM2013-3999