The mir-17~92 cluster encodes six miRNAs encompassing four miRNA seed families (Figure 7A), implicating thousands of predicted mRNA targets as downstream effectors of the cluster's invasive program. To aid in our determination of which miRNA families may be most important in the invasive phenotype, we evaluated nine KPC and nine 17KPC cell lines for their expression of miR-17, -18, -19, and -92 family miRNAs across the three cluster paralogs: mir-17~92, mir-106b~25, and mir-106a~363. Quantitative RT-PCR demonstrated that 17KPC cell lines are indeed null for miRNAs from mir-17~92, however they retain robust expression from mir-106b~25 (Figure 7B, 7C). In fact, the mir-106b~25 locus is sufficient to drive expression of miRNAs for the miR-17 and miR-92 families to levels close to those observed in KPC lines, suggesting that loss of the miR-17 and -92 families may not be primarily responsible for the invasive defect of 17KPC cell lines. In contrast, miR-19 family miRNAs can only be expressed from the mir-17~92 and mir-106a~363 clusters, and 17KPC lines were found to completely lack expression of this miRNA family (Figure 7E). Based on the partial residual expression of the miR-17 and miR-92 families (Figure 7B, 7C), and the generally very low expression of the miR-18 family (Figure 7D, note y axis units), we hypothesized that loss of the miR-19 family was responsible for the defective invasion of 17KPC cell lines.