+47 72573075
Erling Skjalgssons g 1, Laboratoriesenteret * 231.05.036

Background and activities

Research group for:

Regulation of cellular stress and genome dynamics


PCNA (proliferating cell nuclear antigen) and XRCC1 (X-ray repair cross-complementing protein 1) are two essential cellular scaffold proteins important in genome dynamics and cellular homeostasis.  PCNA is a member of the conserved sliding clamp family which in addition to organizing replication also is essential for translesion synthesis (TLS), chromatin remodeling/ epigenetics, DNA repair and recombination1,2. Recently, PCNA has been shown to act as a binding platform also outside the nucleus and independent of chromatin, e.g. PCNA is shown to be involved in regulation of apoptosis3,4, immune response and cellular signaling5-7. XRCC1 is a central scaffold protein in single strand break repair (SSBR) and Base Excision Repair (BER)8. It is a phosphoprotein (> 30 phosphorylation sites) containing several interactions domains important in DNA damage responses (e.g. two BRCT-domains, PAR and FHA binding domains). Recruitment and/or stability of the scaffold proteins XRCC1 and PCNA and their multiple partners is regulated via modifications such as PARylation, phosphorylation and ubiquitinylation, in a highly dynamic process which is vital for the optimal cellular response. This is the primary focus of our research.


APIM-PCNA interactions:

Two PCNA interacting motifs have been identified; the PIP-box 9and the APIM-motif, found by Otterlei and co-workers 1. Like the PIP-box, APIM is found in more than 200 proteins. However, while many of the essential replicative/housekeeping proteins contain the PIP-box and interact with PCNA through this motif, proteins containing APIM are more involved in cellular stress responses, including proteins involved in genome dynamics. Recent publications from us and other research groups support a vital role of APIM-PCNA interactions under cellular stress 1,2,4,5,10-13. We have constructed cell penetrating peptides containing the APIM-sequence (APIM-peptide) that interacts with PCNA, and block interaction of APIM-containing proteins. The hypothesis is that the APIM-peptide impairs the regulatory functions of PCNA, because it blocks “the stress switch” (Figure 1). We have shown that APIM-peptide increase cancer cell´s sensitivity towards more than 20 different cancer drugs while having weaker effects on normal cells. Anti-cancer efficacy is also shown in several preclinical animal models 4,14.



The APIM-peptide therefore impairs the cellular repair and tolerance mechanisms, via inhibiting APIM-containing proteins ability to interact with PCNA (Figure 2), and this sensitizes the cells to various anti-cancer therapies. Cancer cells are more de-regulated and/or stresses and this is likely the reason why they are more sensitive towards the effects of the peptide than normal cells. GLP-toxicology studies in two species have reviled low toxicology of the peptide in rats and dogs. In addition to being a drug candidate, APIM-peptide is a good tool for studying APIM-PCNA interactions’ role in cellular homeostasis, genome stability and genome dynamics.



The phosphoprotein XRCC1 is found in complexes with several glycosylases as well as all proteins needed for the SSBR/BER pathway15, in addition to PCNA16. We originally discovered that the UNG2 glycosylase directly interacted with PCNA (via the PIP-box) and removed misincorporated uracil in a post replicative BER process18. UNG2 also interacts with XRCC115, and XRCC1 are found to be associated with the replication machinery. A model for a two-step post replicative BER-model is suggested (Figure 3).

XRCC1 is a highly dynamic protein which responds to modifications on DNA and cellular stress events within seconds17. These responses, which include both intracellular re-localization, change in protein-protein interactions and protein stability, and are under investigation.



Otterlei is funder of the NTNU-spinoff APIM Therapeutics established 2009.  APIM Therapeutics is developing peptides containing the APIM sequence for use in cancer therapy. Otterlei is CSO in the company. APIM Therapeutics has finished the GLP- toxicology studies required and is now planning for clinical trials (phase I/IIa) in 2016. http://www.apimtherapeutics.com/


1    Gilljam, K. M. et al. Identification of a novel, widespread, and functionally important PCNA-binding motif. J Cell Biol 186, 645-654(2009).

2    Mailand, N., Gibbs-Seymour, I. & Bekker-Jensen, S. Regulation of PCNA-protein interactions for genome stability. Nat Rev Mol Cell Biol 14, 269-282(2013).

3    Witko-Sarsat, V. et al. Proliferating cell nuclear antigen acts as a cytoplasmic platform controlling human neutrophil survival. J Exp Med 207, 2631-2645(2010).

4    Müller, R. et al. Targeting Proliferating Cell Nuclear Antigen and Its Protein Interactions Induces Apoptosis in Multiple Myeloma Cells. PloS one 8, e70430(2013).

5    Olaisen C, M. R., Nedal A, Otterlei M. PCNA-interacting peptides reduce Akt phosphorylation and TLR-mediated cytokine secretion suggesting a role of PCNA in cellular signaling. Cell Signal 27, 14789-87 (2015).

6    Rosental, B. et al. Proliferating Cell Nuclear Antigen Is a Novel Inhibitory Ligand for the Natural Cytotoxicity Receptor NKp44. J. Immunol. 187, 5693-5702(2011).

7    Naryzhny, S. N. & Lee, H. Proliferating cell nuclear antigen in the cytoplasm interacts with components of glycolysis and cancer. FEBS Lett 584, 4292-4298(2010).

8    Hanssen-Bauer, A., Solvang-Garten, K., Akbari, M. & Otterlei, M. X-ray repair cross complementing protein 1 in base excision repair. International journal of molecular sciences 13, 17210-17229(2012).

9    Warbrick, E. The puzzle of PCNA's many partners. Bioessays 22, 997-1006(2000).

10  Bacquin, A. et al. The helicase FBH1 is tightly regulated by PCNA via CRL4 (Cdt2)-mediated proteolysis in human cells. Nucleic acids research(2013).

11  Ciccia, A. et al. Polyubiquitinated PCNA recruits the ZRANB3 translocase to maintain genomic integrity after replication stress. Molecular cell 47, 396-409(2012).

12  Gilljam, K. M., Muller, R., Liabakk, N. B. & Otterlei, M. Nucleotide Excision Repair Is Associated with the Replisome and Its Efficiency Depends on a Direct Interaction between XPA and PCNA. PloS one 7, e49199(2012).

13  Fattah, F. J. et al. The transcription factor TFII-I promotes DNA translesion synthesis and genomic stability. PLoS genetics 10, e1004419(2014).

14  Gederaas, O. A. et al. Increased Anticancer Efficacy of Intravesical Mitomycin C Therapy when Combined with a PCNA Targeting Peptide. Translational oncology 7, 812-823(2014).

15  Akbari, M. et al. Direct interaction between XRCC1 and UNG2 facilitates rapid repair of uracil in DNA by XRCC1 complexes. DNA Repair (Amst) 9, 785-795(2010).

16  Fan, J., Otterlei, M., Wong, H. K., Tomkinson, A. E. & Wilson, D. M., 3rd. XRCC1 co-localizes and physically interacts with PCNA. Nucleic Acids Res. 32, 2193-2201(2004).

17  Hanssen-Bauer, A. et al. XRCC1 coordinates disparate responses and multiprotein repair complexes depending on the nature and context of the DNA damage. Environ Mol Mutagen 52, 623-635(2011).

18  Otterlei, M. et al. Post-replicative base excision repair in replication foci. EMBO J. 18, 3834-3844(1999).










Scientific, academic and artistic work

A selection of recent journal publications, artistic productions, books, including book and report excerpts. See all publications in the database

Journal publications