Krüppel-like Factor-9 and Krüppel-like Factor-13: Highly Related, Multi-Functional, Transcriptional Repressors and Activators of Oncogenesis

Simple Summary Kruppel-like Factor-9 (KLF9) and Kruppel-like Factor-13 (KLF13) are highly related proteins that function as inducers and/or repressors of specific target gene repertoires in a variety of tissues and in diverse pathophysiological states, including neoplasia. Here, we describe the salient features of KLF9 and KLF13, the current state-of-the-art research regarding both protein's actions in cancer development and response to therapies, and where the field requires further exploration. These paralogous proteins warrant further study for multiple cancers, and with respect to their multiplicities of action in suppression or promotion of proliferative and metastatic phenotypes, and likely involvement in immune cell biology within the tumor microenvironment.Abstract Specificity Proteins/Kruppel-like Factors (SP/KLF family) are a conserved family of transcriptional regulators. These proteins share three highly conserved, contiguous zinc fingers in their carboxy-terminus, requisite for binding to cis elements in DNA. Each SP/KLF protein has unique primary sequence within its amino-terminal and carboxy-terminal regions, and it is these regions which interact with co-activators, co-repressors, and chromatin-modifying proteins to support the transcriptional activation and repression of target genes. Kruppel-like Factor 9 (KLF9) and Kruppel-like Factor 13 (KLF13) are two of the smallest members of the SP/KLF family, are paralogous, emerged early in metazoan evolution, and are highly conserved. Paradoxically, while most similar in primary sequence, KLF9 and KLF13 display many distinct roles in target cells. In this article, we summarize the work that has identified the roles of KLF9 (and to a lesser degree KLF13) in tumor suppression or promotion via unique effects on differentiation, pro- and anti-inflammatory pathways, oxidative stress, and tumor immune cell infiltration. We also highlight the great diversity of miRNAs, lncRNAs, and circular RNAs which provide mechanisms for the ubiquitous tumor-specific suppression of KLF9 mRNA and protein. Elucidation of KLF9 and KLF13 in cancer biology is likely to provide new inroads to the understanding of oncogenesis and its prevention and treatments.

Automated summary

KLF9 and KLF13 are related proteins that play roles as regulators of specific target genes in various tissues and pathophysiological states, including cancer development. They have diverse functions in tumor suppression or promotion, differentiation, inflammatory pathways, oxidative stress, and tumor immune cell infiltration. The study of KLF9 and KLF13 in cancer biology is likely to provide valuable insights into oncogenesis and its prevention and treatments.